ItaLynch: an ongoing Italian study to evaluate the feasibility of mainstreaming the diagnosis of Lynch syndrome in colorectal cancer patients

•This is a prospective, observational, multicenter, multidisciplinary, Italian study. •We investigate the feasibility of a new diagnostic algorithm for LS. •A 'Lynch alert' in the pathology report is used as a clear warning to clinicians. •We propose a shift to an oncologist-led mainstreaming genetic testing. •This study encourages the establishment of multidisciplinary workgroups. BackgroundInternational guidelines recommend universal screening for Lynch syndrome (LS) through somatic DNA mismatch repair deficiency (dMMR) testing in all colorectal cancers (CRCs). However, LS remains largely underdiagnosed. Mainstreaming LS diagnosis through oncologist-driven genetic testing could increase detection rates, thus extending the benefits of precision prevention to patients with LS and their families. We aim to evaluate the feasibility of the mainstreaming diagnostic algorithm for LS. Patients and methodsItaLynch is an ongoing, prospective, observational, multicenter, multidisciplinary, Italian study in patients with dMMR CRC. Being descriptive in nature, it does not attempt to test any specific, a priori, hypothesis. Patients with dMMR CRC are selected by universal screening by immunohistochemistry (IHC). In MLH1-deficient patients, reflex testing for BRAFV600E and, when appropriate, for MLH1 promoter hypermethylation is carried out. For all dMMR CRC, a 'Lynch Alert' is added to the pathology report: positive when a patient is at high risk for LS, due to reflex testing results or to loss of non-MLH1 proteins. Conversely, a 'Lynch Alert' is negative when the patient is likely to be a nonhereditary case (i. e. MLH1 loss and BRAFV600E or MLH1 promoter hypermethylation). In patients with a positive 'Lynch Alert', after providing a brief explanation about the risks and benefits of genetic testing, the oncologist asks patients for their consent to mainstream genetic testing. Thus a blood sample is drawn for constitutional variants of the MMR genes. Carriers of a germline variant are then referred to post-test genetic counseling. Referral to clinical genetic services is also advised for patients with clinical suspect criteria. International guidelines recommend universal screening for Lynch syndrome (LS) through somatic DNA mismatch repair deficiency (dMMR) testing in all colorectal cancers (CRCs). However, LS remains largely underdiagnosed. Mainstreaming LS diagnosis through oncologist-driven genetic testing could increase detection rates, thus extending the benefits of precision prevention to patients with LS and their families. We aim to evaluate the feasibility of the mainstreaming diagnostic algorithm for LS. ItaLynch is an ongoing, prospective, observational, multicenter, multidisciplinary, Italian study in patients with dMMR CRC. Being descriptive in nature, it does not attempt to test any specific, a priori, hypothesis. Patients with dMMR CRC are selected by universal screening by immunohistochemistry (IHC). In MLH1-deficient patients, reflex testing for BRAFV600E and, when appropriate, for MLH1 promoter hypermethylation is carried out. For all dMMR CRC, a 'Lynch Alert' is added to the pathology report: positive when a patient is at high risk for LS, due to reflex testing results or to loss of non-MLH1 proteins. Conversely, a 'Lynch Alert' is negative when the patient is likely to be a nonhereditary case (i. e. MLH1 loss and BRAFV600E or MLH1 promoter hypermethylation). In patients with a positive 'Lynch Alert', after providing a brief explanation about the risks and benefits of genetic testing, the oncologist asks patients for their consent to mainstream genetic testing. Thus a blood sample is drawn for constitutional variants of the MMR genes. Carriers of a germline variant are then referred to post-test genetic counseling. Referral to clinical genetic services is also advised for patients with clinical suspect criteria. Colorectal cancer (CRC) is the third most common type of cancer diagnosed and the second leading cause of cancer death worldwide. 1Sung H. Ferlay J. Siegel R. L. et al. Global cancer statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin. 2021; 71: 209-249Crossref PubMed Scopus (48234) Google Scholar In Italy, CRC is the second most frequently diagnosed and the second leading cause of cancer death. 2AIOM (Associazione Italiana di Oncologia Medica) I numeri del cancro in Italia 2022; 2022. https: //www. aiom. it/wp-content/uploads/2022/12/2022AIOMNDC-web. pdfDate accessed: February 6, 2024Google Scholar Overall, ∼15% of all patients with CRC (stage I-IV) have DNA mismatch repair deficiency (dMMR), which results in high microsatellite instability (MSI-H). 3Jin Z. Sinicrope F. A. Mismatch repair-deficient colorectal cancer: building on checkpoint blockade. J Clin Oncol. 2022; 40: 2735-2750Crossref PubMed Scopus (46) Google Scholar Of note, the prevalence of dMMR varies according to stage and location. Indeed, among patients with CRC, dMMR prevalence is higher in early stages and decreased in advanced disease (20% in stage I-II, 12% in stage III, and 4% in stage IV). Moreover, the prevalence of dMMR in rectal cancer is ∼3%. 4Papke Jr. , D. J. Yurgelun M. B. Noffsinger A. E. Turner K. O. Genta R. M. Redston M. Prevalence of mismatch-repair deficiency in rectal adenocarcinomas. N Engl J Med. 2022; 387: 1714-1716Crossref PubMed Scopus (0) Google Scholar Among patients with dMMR CRC, ∼20% are affected by Lynch syndrome (LS). 5Latham A. Srinivasan P. Kemel Y. et al. Microsatellite instability is associated with the presence of Lynch syndrome pan-cancer. J Clin Oncol. 2019; 37: 286-295Crossref PubMed Scopus (339) Google Scholar This estimate suggests that the prevalence of LS among all patients with CRC is ∼3%. LS is a common inherited cancer predisposition disorder estimated to affect 1 in 279 individuals worldwide. 6Win A. K. Jenkins M. A. Dowty J. G. et al. Prevalence and penetrance of major genes and polygenes for colorectal cancer. Cancer Epidemiol Biomarkers Prev. 2017; 26: 404-412Crossref PubMed Scopus (287) Google Scholar The syndrome is caused by germline pathogenic variants in DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, or PMS2) or the EPCAM gene. 7Sinicrope F. A. Lynch syndrome–associated colorectal cancer. N Engl J Med. 2018; 379: 764-773Crossref PubMed Scopus (150) Google Scholar In LS, lifetime risks are highest for CRC and endometrial cancers; the risks of ovarian, stomach, small bowel, urothelial, pancreaticobiliary, and brain cancers are also increased compared with the general population. 5Latham A. Srinivasan P. Kemel Y. et al. Microsatellite instability is associated with the presence of Lynch syndrome pan-cancer. J Clin Oncol. 2019; 37: 286-295Crossref PubMed Scopus (339) Google Scholar, 8Kupfer S. S. Broadening our understanding of the immune landscape in Lynch syndrome. Gastroenterology. 2022; 162: 1024-1025Abstract Full Text Full Text PDF Scopus (2) Google Scholar Patients with LS-associated CRC seem to have a better prognosis compared with patients with sporadic CRC. 9Phipps A. I. Limburg P. J. Baron J. A. et al. Association between molecular subtypes of colorectal cancer and patient survival. Gastroenterology. 2015; 148: 77-87. e72Abstract Full Text Full Text PDF PubMed Scopus (319) Google Scholar, 10Chalabi M. Verschoor Y. L. van den Berg J. et al. LBA7 neoadjuvant immune checkpoint inhibition in locally advanced MMR-deficient colon cancer: the NICHE-2 study. Ann Oncol. 2022; 33: S1389Abstract Full Text Full Text PDF Google Scholar Furthermore, patients with LS require personalized treatment and benefit from enrollment in targeted surveillance protocols for metachronous primary CRCs and other syndrome-associated cancers. 11Stoffel E. M. Mangu P. B. Gruber S. B. et al. Hereditary colorectal cancer syndromes: American Society of Clinical Oncology Clinical Practice Guideline endorsement of the familial risk-colorectal cancer: European Society for Medical Oncology Clinical Practice Guidelines. J Clin Oncol. 2015; 33: 209-217Crossref PubMed Google Scholar Identifying the at-risk relatives of patients with LS and enrolling them in surveillance programs also leads to early diagnosis of LS-associated cancers, reducing mortality by ∼60%. 12Jarvinen H. J. Renkonen-Sinisalo L. Aktan-Collan K. Peltomäki P. Aaltonen L. A. Mecklin J. P. Ten years after mutation testing for Lynch syndrome: cancer incidence and outcome in mutation-positive and mutation-negative family members. J Clin Oncol. 2009; 27: 4793-4797Crossref PubMed Scopus (229) Google Scholar The clinical diagnosis of LS used to be based on clinical features, including family history of cancer, and pathological findings (Amsterdam criteria 1990 and Bethesda criteria 1997). 13Lynch syndrome (hereditary nonpolyposis colorectal cancer syndrome). in: Greenson J. K. Lauwers G. Y. Montgomery E. A. Diagnostic Pathology: Gastrointestinal. 2nd ed. Elsevier, Philadelphia, PA2016: 498-499Google Scholar, 14Lipton L. R. Johnson V. Cummings C. et al. Refining the Amsterdam Criteria and Bethesda Guidelines: testing algorithms for the prediction of mismatch repair mutation status in the familial cancer clinic. J Clin Oncol. 2004; 22: 4934-4943Crossref PubMed Scopus (80) Google Scholar However, these diagnostic criteria fail to recognize LS in ∼25% of cases, 15Hampel H. Frankel W. L. Martin E. et al. Feasibility of screening for Lynch syndrome among patients with colorectal cancer. J Clin Oncol. 2008; 26: 5783-5788Crossref PubMed Scopus (720) Google Scholar, 16Giardiello F. M. Allen J. I. Axilbund J. E. et al. Guidelines on genetic evaluation and management of Lynch syndrome: a consensus statement by the US Multi-Society Task Force on colorectal cancer. Gastroenterology. 2014; 147: 502-526Abstract Full Text Full Text PDF PubMed Scopus (355) Google Scholar likely due to their complexity and to the fact that accurate family histories are seldom available. Therefore universal screening of LS through the identification of MMR deficiency in the tumor tissue of all CRC cases has been proposed as an alternative diagnostic approach since 2008. 17Sepulveda A. R. Hamilton S. R. Allegra C. J. et al. Molecular biomarkers for the evaluation of colorectal cancer: guideline from the American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology, and the American Society of Clinical Oncology. J Clin Oncol. 2017; 35: 1453-1486Crossref PubMed Scopus (239) Google Scholar The universal screening for LS18Stjepanovic N. Moreira L. Carneiro F. et al. Hereditary gastrointestinal cancers: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2019; 30: 1558-1571Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, 19Giardiello F. M. Allen J. I. Axilbund J. E. et al. Guidelines on genetic evaluation and management of Lynch syndrome: a consensus statement by the US Multi-society Task Force on colorectal cancer. Am J Gastroenterol. 2014; 109: 1159-1179Crossref PubMed Scopus (344) Google Scholar, 20Syngal S. Brand R. E. Church J. M. et al. ACG clinical guideline: genetic testing and management of hereditary gastrointestinal cancer syndromes. Am J Gastroenterol. 2015; 110 (; quiz 263): 223-262Crossref PubMed Google Scholar includes IHC test to evaluate MMR protein expression loss or a molecular test to assess MSI. 17Sepulveda A. R. Hamilton S. R. Allegra C. J. et al. Molecular biomarkers for the evaluation of colorectal cancer: guideline from the American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology, and the American Society of Clinical Oncology. J Clin Oncol. 2017; 35: 1453-1486Crossref PubMed Scopus (239) Google Scholar, 21NICE | The National Institute for Health and Care ExcellenceMolecular testing strategies for Lynch syndrome in people with colorectal cancer. Diagnostics guidance. www. nice. org. uk/guidance/dg27Date: 2017Date accessed: February 6, 2024Google Scholar Multiple societies currently recommend testing for patients with newly diagnosed CRC, and this is now the standard of care. 22Adar T. Rodgers L. H. Shannon K. M. et al. Universal screening of both endometrial and colon cancers increases the detection of Lynch syndrome. Cancer. 2018; 124: 3145-3153Crossref PubMed Scopus (62) Google Scholar Overall, IHC is to be preferred over the MSI test because it is cheaper and more widely available; it can also predict good response to treatment with immune checkpoint inhibitors in patients with advanced cancer. 23Le D. T. Durham J. N. Smith K. N. et al. Mismatch repair deficiency predicts response of solid tumors to PD-1 blockade. Science. 2017; 357: 409-413Crossref PubMed Scopus (4513) Google Scholar, 24Le D. T. Uram J. N. Wang H. et al. PD-1 blockade in tumors with mismatch-repair deficiency. N Engl J Med. 2015; 372: 2509-2520Crossref PubMed Scopus (6981) Google Scholar Finally, it is more informative than the MSI test, as it is able to distinguish which of the four MMR proteins is involved, thereby guiding reflex testing, genetic counseling, and genetic testing. 25Zhang X. Li J. Era of universal testing of microsatellite instability in colorectal cancer. World J Gastrointest Oncol. 2013; 5: 12-19Crossref PubMed Google Scholar Genetic counseling and testing are always recommended for patients with CRC with MSH2, MSH6, or PMS2 protein expression loss, given that they are likely to be affected by LS. 26Sinicrope F. A. Foster N. R. Thibodeau S. N. et al. DNA mismatch repair status and colon cancer recurrence and survival in clinical trials of 5-fluorouracil-based adjuvant therapy. J Natl Cancer Inst. 2011; 103: 863-875Crossref PubMed Scopus (418) Google Scholar CRCs with MLH1 protein expression loss, who account for the vast majority of patients with dMMR CRC, are instead more frequently nonhereditary, due to somatic epigenetic inactivation of the MLH1 gene. As the presence of somatic BRAFV600E mutation and/or hypermethylation of the MLH1 promoter are indicative of a very low likelihood of LS, reflex tumor testing has been implemented to better select patients with MLH1 loss for genetic counseling and testing. 27Puccini A. Nardin S. Trevisan L. et al. Streamlining the diagnostic pathway for Lynch syndrome in colorectal cancer patients: a 10-year experience in a single Italian Cancer Center. Eur J Cancer Prev. 2024; https: //doi. org/10. 1097/CEJ. 0000000000000870Crossref Google Scholar Several strategies have been investigated for cost-effectiveness by the National Institute for Health and Care Excellence (NICE), which suggests that strategies beginning with IHC for MMR proteins are more cost-effective than those beginning with MSI testing, and that overall, reflex testing conducted as described below appears to be the most cost-effective approach21NICE | The National Institute for Health and Care ExcellenceMolecular testing strategies for Lynch syndrome in people with colorectal cancer. Diagnostics guidance. www. nice. org. uk/guidance/dg27Date: 2017Date accessed: February 6, 2024Google Scholar: The IHC four-panel test for MLH1, MSH2, MSH6, and PMS2, then: •genetic testing for abnormal MSH2, MSH6, or PMS2 IHC results, or•BRAFV600E testing for an abnormal MLH1 IHC result; if negative, then MLH1 promoter hypermethylation testing is carried out; if the MLH1 promoter is not hypermethylated, genetic testing is carried out. The identification of patients whose cancer is associated with an underlying predisposition syndrome allows for improved understanding and management of their own and their relatives' future cancer risk. Increasingly, it also has an impact on their treatment. Considering the potential benefits for both treatment and prevention, National Comprehensive Cancer Network (NCCN) guidelines have endorsed germline genetic testing for all patients with certain cancer types (epithelial ovarian cancer, exocrine metastatic pancreatic cancer, and high-grade/metastatic prostate cancer), regardless of age or personal/family history of cancer. 28NCCNNational Comprehensive Cancer Network (NCCN) guidelines. https: //www. nccn. org/guidelines/category₁Date accessed: February 6, 2024Google Scholar However, ensuring appropriate and equitable access to genetic counseling and testing remains a challenge, as increased referral volumes have translated into over-burdened genetic services and longer waiting times for access to genetic counseling. An alternative model, named 'mainstreaming cancer genetics', was therefore developed29George A. Riddell D. Seal S. et al. Implementing rapid, robust, cost-effective, patient-centred, routine genetic testing in ovarian cancer patients. Sci Rep. 2016; 629506Crossref Scopus (154) Google Scholar, 30Hampel H. Yurgelun M. B. Point/counterpoint: is it time for universal germline genetic testing for all GI cancers? . J Clin Oncol. 2022; 40: 2681-2692Crossref PubMed Scopus (13) Google Scholar, 31Rumford M. Lythgoe M. McNeish I. et al. Oncologist-led BRCA 'mainstreaming' in the ovarian cancer clinic: a study of 255 patients and its impact on their management. Sci Rep. 2020; 10: 3390Crossref PubMed Scopus (34) Google Scholar, 32Rahman B. Lanceley A. Kristeleit R. S. et al. Mainstreamed genetic testing for women with ovarian cancer: first-year experience. J Med Genet. 2019; 56: 195-198Crossref PubMed Scopus (42) Google Scholar and successfully trialed. 33Colombo N. Huang G. Scambia G. et al. Evaluation of a streamlined oncologist-led BRCA mutation testing and counseling model for patients with ovarian cancer. J Clin Oncol. 2018; 36: 1300-1307Crossref PubMed Scopus (74) Google Scholar It has been shown that it can improve access to hereditary cancer genetic testing in patients with breast and ovarian cancer by shifting genetic testing from genetic services to oncology clinics, enabling oncologists to discuss and initiate genetic testing with selected patients with cancer. Recently, a systematic review has shown that mainstream genetic testing seems feasible in daily practice, with no insurmountable barriers. A structured pathway with a training procedure is desirable, as well as close collaboration between genetics and other clinical departments. 34Bokkers K. Vlaming M. Engelhardt E. G. et al. The feasibility of implementing mainstream germline genetic testing in routine cancer care—a systematic review. Cancers (Basel). 2022; 14: 1059Crossref PubMed Scopus (0) Google Scholar To maximize availability, utility, and equity of access to genetic testing for LS, all patients found to be at risk for LS by reflex testing could be offered genetic testing by oncologists. Based on this background, the overall goal of our study is to evaluate the feasibility and performance of an oncologist-driven diagnostic algorithm for LS (mainstreaming) in patients with CRC. In the traditional diagnostic pathway for LS, genetic counseling and testing are always recommended for patients with CRC in whom loss of expression of one of the proteins encoded by the MSH2, MSH6, or PMS2 genes is detected. Identifying which patients with MLH1 protein expression loss (who account for ∼80% of all dMMR cases) should be offered genetic counseling and genetic testing is not straightforward, as protein expression loss in most of these patients is not caused by a germline pathogenic variant, 15Hampel H. Frankel W. L. Martin E. et al. Feasibility of screening for Lynch syndrome among patients with colorectal cancer. J Clin Oncol. 2008; 26: 5783-5788Crossref PubMed Scopus (720) Google Scholar but rather by somatic epigenetic methylation of the MLH1 promoter. Moreover, CRCs in LS carriers do not usually display a BRAFV600E mutation. 17Sepulveda A. R. Hamilton S. R. Allegra C. J. et al. Molecular biomarkers for the evaluation of colorectal cancer: guideline from the American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology, and the American Society of Clinical Oncology. J Clin Oncol. 2017; 35: 1453-1486Crossref PubMed Scopus (239) Google Scholar, 21NICE | The National Institute for Health and Care ExcellenceMolecular testing strategies for Lynch syndrome in people with colorectal cancer. Diagnostics guidance. www. nice. org. uk/guidance/dg27Date: 2017Date accessed: February 6, 2024Google Scholar Therefore, in case of MLH1 loss, genetic counseling and genetic testing are usually recommended only for patients with BRAF wild-type with no hypermethylation of the MLH1 promoter. International guidelines (NCCN) do not detail the role of different health care professionals in the decisional algorithm leading to a diagnosis of LS. BRAFV600E testing carried out routinely by the pathologist in all MLH1-deficient tumors has been found to determine a 40% reduction in referrals to genetic clinics, improving the appropriateness of referrals, leading to time and cost savings, and sparing unnecessary alarm to patients. 35Jin M. Hampel H. Zhou X. Schunemann L. Yearsley M. Frankel W. L. BRAF V600E mutation analysis simplifies the testing algorithm for Lynch syndrome. Am J Clin Pathol. 2013; 140: 177-183Crossref PubMed Scopus (41) Google Scholar Moreover, the evaluation of MLH1 hypermethylation has been reported to potentially spare an additional 60% of patients with BRAF wild-type the need for genetic counseling. 36Adar T. Rodgers L. H. Shannon K. M. et al. A tailored approach to BRAF and MLH1 methylation testing in a universal screening program for Lynch syndrome. Mod Pathol. 2017; 30: 440-447Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar Preliminary data from our study conducted on ∼1500 patients at IRCCS Policlinico San Martino in Genoa showed that the rate of referral of patients with dMMR CRC to pretest genetic counseling by oncologists is low (only 20%). Moreover, we observed that if pretest counseling had been offered only to the patients with BRAF wild-type with MLH1 loss, 57% of the pretest counseling sessions conducted could have been avoided, increasing the genetic counseling yield in terms of LS diagnosis by 75%. 37Sciallero S. Damiani A. Zupo S. et al. Streamlining universal screening for lynch syndrome (LS): towards improved yield of genetic counseling (GC). J Clin Oncol. 2019; 37: 503Crossref Google Scholar, 38Puccini A. Damiani A. Varesco L. et al. PD-9 universal screening for Lynch syndrome: reflex testing to improve appropriateness of genetic counseling and diagnosis. Ann Oncol. 2020; 31: S214-S215Abstract Full Text Full Text PDF Google Scholar Taken together, these findings suggest that incorporating genetic testing in an oncologist-driven diagnostic algorithm for LS could increase diagnostic rates, offering the benefits of precision medicine and a streamlined pathway of care to patients with LS and their families. 39Wright S. Porteous M. Stirling D. et al. Patients' views of treatment-focused genetic testing (TFGT): some lessons for the mainstreaming of BRCA1 and BRCA2 testing. J Genet Couns. 2018; 27: 1459-1472Crossref PubMed Scopus (0) Google Scholar, 40Slade I. Riddell D. Turnbull C. Hanson H. Rahman N. MCG ProgrammeDevelopment of cancer genetic services in the UK: a national consultation. Genome Med. 2015; 7: 18Crossref PubMed Google Scholar This is a prospective, observational, multicenter, Italian study of patients diagnosed with dMMR/MSI-H CRC. The study is descriptive in nature and does not attempt to test any specific a priori hypotheses. Patients are recruited from participating sites from all over Italy. Our multidisciplinary project involves oncologists, pathologists, molecular biologists, gastroenterologists, and geneticists to make LS diagnosis as universal and simple as possible in all participating centers. We have established a nation-wide network across Italian centers, involving those able to carry out IHC analysis of MMR protein in all patients with stage I-IV CRC (LS universal screening) and that already have well-established links with medical genetics services. Patients in whom CRC tumor samples are found to be dMMR/MSI-H at each participating site are enrolled in the study according to the inclusion/exclusion criteria, after informed consent. BRAFV600E mutation and MLH1 hypermethylation are evaluated in MLH1-deficient patients at all centers, in accordance with the reflex testing model. For all patients with dMMR/MSI-H CRC, a 'Lynch Alert' is added to the pathology report, warning oncologists and/or gastroenterologists about the patient's risk of being affected by LS or not. We define a 'Lynch alert' as positive when a patient with dMMR/MSI-H is at high risk for LS, due to the results of reflex testing or to loss of non-MLH1 proteins. Conversely, a negative 'Lynch alert' is added to the pathology report when the patient is likely to be a nonhereditary dMMR/MSI-H case (i. e. MLH1 loss and BRAFV600E mutation or MLH1 promoter hypermethylation). After providing a brief explanation about the risks and benefits of genetic testing, possible results, and their implications, oncologists and/or gastroenterologists ask patients with a positive 'Lynch Alert' for their consent to mainstream genetic testing. If the patient consents, a blood sample is drawn to search for constitutive variants of the MLH1, MSH2, MSH6, and PMS2 genes. Standard site-specific procedures (e. g. informed consent forms for routine genetic testing and transfer of blood sample to testing laboratory) are employed by all centers. Blood samples are analyzed by local medical genetics laboratories, which return the results to treating oncologists and/or gastroenterologists. This avoids referring all patients with dMMR for pretest genetic counseling. Participants in whom a pathogenic variant of one of the MMR genes is detected are referred for post-test genetic counseling. Every patient found to be: •MMR proficient or•not eligible for genetic testing (dMMR with an MLH1 deficiency and a BRAFV600E mutation or MLH1 hypermethylation—negative 'Lynch Alert') or•with a negative genetic test result is considered unlikely to be affected by LS. Nevertheless, to rule out the presence of a hereditary cancer syndrome, oncologists and/or gastroenterologists administer a validated family history questionnaire to all participants. Participants whose questionnaire results suggest the presence of a hereditary cancer syndrome are referred to genetic counseling. Participants who wish to receive more in-depth information about their genetic risk are also referred to genetic counseling. In addition, all ItaLynch participants found to harbor variants of uncertain significance are referred for post-test counseling. In addition, a parallel study on variants of uncertain significance is being carried out by the geneticists involved in the ItaLynch study. Most oncology units included in this project participated in the TOSCA Trial, sponsored and coordinated by the Italian Group for the study of gastrointestinal cancers (GISCAD), the first trial to be conducted and completed among the international IDEA trials on adjuvant colon cancer treatment. 41Sobrero A. Lonardi S. Rosati G. et al. FOLFOX or CAPOX in stage II to III colon cancer: efficacy results of the Italian three or six colon adjuvant trial. J Clin Oncol. 2018; 36: 1478-1485Crossref PubMed Scopus (53) Google Scholar, 42Grothey A. Sobrero A. F. Shields A. F. et al. Duration of adjuvant chemotherapy for stage III colon cancer. N Engl J Med. 2018; 378: 1177-1188Crossref PubMed Scopus (631) Google Scholar The results of these studies led to a paradigm shift in the treatment of patients with early-stage colon cancer worldwide. Such an accomplishment was made possible thanks to the close, successful cooperation among groups from all over Italy and coordination by the GISCAD group which allowed us to enroll ∼3700 patients with colon cancer. The start day of the study was 1 March 2021, which is the day the study was approved by the Ethics Committee of the Coordinating Center in Genoa, Italy. The project will continue to prospectively enroll patients in for 48 months overall, so the planned end date will be in March 2025. The primary objectives of the study are as follows: •To estimate the frequency of LS among patients with dMMR CRC. •To evaluate the feasibility of the mainstreaming diagnostic algorithm for LS. •To estimate the extent to which the mainstreaming approach reduces the workload of specialist genetics services compared with the traditional genetic counseling model. •To measure patients', oncologists', and geneticists' satisfaction with the mainstreaming approach. •Proportion of LS diagnosis among patients with dMMR/MSI-H enrolled in the study. •Proportion of: •BRAFV600E testing among MLH1-deficient cases. •MLH1 promoter hypermethylation testing among BRAF wild-type cases. •'Lynch Alert' addenda in the histology report of all dMMR/MSI-H cases. •Oncologist/gastroenterologist-led mainstream genetic testing among participants with a positive 'Lynch Alert'. •Participants agreeing to have clinical genetic testing among those invited within the oncologist/gastroenterologist-led mainstream genetic testing process. •Oncologist/gastroenterologist referring participants with a positive genetic test result for post-test counseling. •Participants agreeing to post-test genetic counseling. •Participants presenting to post-test genetic counseling. •Ratio of: •Post-test genetic counseling sessions following the mainstream diagnostic process compared with the estimated number of post-test genetic counseling sessions according to the classical diagnostic model. •Patients requesting referral to pretest genetic counseling among those offered genetic testing by oncologists/gastroenterologists. •Patients requesting referral to post-test genetic counseling among those with negative genetic testing. •Satisfaction of: •Patients after mainstream pretest counseling, using the Oncogenetic Counseling Elements Questionnaire. •Patients after genetic testing, using the Modified Royal Marsden Patient Satisfaction Questionnaire. •Oncologists, using the Oncologist Satisfaction Survey. •Geneticists, using the Genetic Counselor Satisfaction Survey. •Histologically