Updated Protocol for the Examination of Specimens From Patients With Carcinomas of the Colon and Rectum, Excluding Carcinoid Tumors, Lymphomas, Sarcomas, and Tumors of the Vermiform Appendix

This protocol is intended to assist pathologists in providing clinically useful and relevant information as a result of the examination of surgical specimens. Use of this protocol is intended to be entirely voluntary. If equally valid protocols or similar documents are applicable, the pathologist is, of course, free to follow those authorities. Indeed, the ultimate judgment regarding the propriety of any specific procedure must be made by the physician in light of the individual circumstances presented by a specific patient or specimen.It should be understood that adherence to this protocol will not guarantee a successful result. Nevertheless, pathologists are urged to familiarize themselves with the document. Should a physician choose to deviate from the protocol based on the circumstances of a particular patient or specimen, the physician is advised to make a contemporaneous written notation of the reason for the procedure followed.The College recognizes that this document may be used by hospitals, attorneys, managed care organizations, insurance carriers, and other payers. However, the document was developed solely as a tool to assist pathologists in the diagnostic process by providing information that reflects the state of relevant medical knowledge at the time the protocol was first published. It was not developed for credentialing, litigation, or reimbursement purposes. The College cautions that any uses of the protocol for these purposes involve considerations that are beyond the scope of this document.The protocol applies to all carcinomas arising in the colon and rectum.1The colon is divided into 4 parts: the right (ascending), the middle (transverse), the left (descending), and the sigmoid. The right colon is subdivided into the cecum (peritoneally located and measuring about 6 × 9 cm) and the ascending colon (located retroperitoneally and measuring 15 to 20 cm long). The descending colon, also located retroperitoneally, is 10 to 15 cm in length. The descending colon becomes the sigmoid colon at the origin of the mesosigmoid, and the sigmoid colon becomes the rectum at the termination of the mesosigmoid. The upper third of the rectosigmoid segment is covered by peritoneum on the front and both sides. The middle third is covered by peritoneum only on the anterior surface. The lower third (also known as the rectum or rectal ampulla) has no peritoneal covering.1Tumors located at the border between 2 subsites of the colon (eg, cecum and ascending colon) are registered as tumors of the subsite that is more involved. If 2 subsites are involved to the same extent, the tumor is classified as an "overlapping" lesion. The rectum is defined clinically as the distal large intestine, which commences opposite the sacral promontory and ends at the upper border of the anal canal. When measuring below with a rigid sigmoidoscope, it extends 16 cm from the anal verge. A tumor is classified as rectal if its inferior margin lies less than 16 cm from the anal verge or if any part of the tumor is located at least partly within the supply of the superior rectal artery.2 A tumor is classified as rectosigmoid when differentiation between rectum and sigmoid, according to these guidelines, is not possible.3For consistency in reporting, the histologic classification proposed by the World Health Organization is recommended.4 However, this protocol does not preclude the use of other systems of classification or histologic types.World Health Organization Classification of Colorectal CarcinomaAdenocarcinoma in situ/severe dysplasia*AdenocarcinomaMedullary carcinoma†Mucinous (colloid) adenocarcinoma (>50% mucinous)‡Signet-ring cell carcinoma (>50% signet-ring cells)§Squamous cell (epidermoid) carcinomaAdenosquamous carcinomaSmall cell (oat cell) carcinoma§Undifferentiated carcinoma§Other (specify)∥* To avoid confusion with the term carcinoma in situ as it applies to pTis in the TNM staging (see note F), the term intraepithelial carcinoma should be used to refer to histologically malignant epithelium that does not penetrate the basement membrane (ie, shows no evidence of stromal lamina propria invasion).5,6† Medullary carcinoma has been added to the revised World Health Organization histologic classification that will be published in 2000. Medullary carcinoma is a histologic type that is strongly associated with a high degree of microsatellite instability (MSI-H) indicative of loss of normal DNA repair gene function.6–8 With loss of function of any of the genes involved in the repair of mitosis-associated mistakes in DNA synthesis (ie, replication errors), mutations in daughter cells are rapidly accumulated. Ultimately, tumors with defective DNA repair acquire inactivating mutations of genes necessary for complex biological activities such as metastasis. For this reason, tumors with MSI-H, such as most (if not all) medullary carcinomas, have a favorable prognosis compared with microsatellite stable tumors or tumors with low levels of microsatellite instability. Medullary carcinoma may occur either sporadically7 or in association with the hereditary nonpolyposis colon cancer syndrome.8 This tumor type is characterized by uniform polygonal tumor cells that exhibit solid growth in nested, organoid, or trabecular patterns and that only focally produce small amounts of mucin. In addition, medullary carcinomas are typically infiltrated by lymphocytes (tumor-infiltrating lymphocytes) and have no immunohistochemical evidence of neuroendocrine differentiation.‡ In most previous studies on prognostic factors in colorectal cancer, the impact of genetic status (ie, loss of DNA repair gene function with microsatellite instability) on the relationship between histologic type and outcome has not been considered. This shortfall is particularly relevant to mucinous carcinoma, a histologic type that is common among tumors with MSI-H. Overall, most mucinous carcinomas are microsatellite stable. Thus, it is not surprising that the prognostic significance of mucinous carcinoma has proven controversial.6,9 A few studies, largely limited to univariate analyses, have indicated that mucinous adenocarcinoma may be an adverse prognostic factor. Alternatively, mucinous carcinoma has been linked with adverse outcome only when occurring in specific anatomic regions of the bowel (eg, the rectosigmoid) or in a specific subset of patients (ie, those younger than 45 years). In yet other studies, mucinous carcinoma has been linked to adverse outcome only when mucinous and signet-ring cell carcinomas have been grouped together and compared with typical adenocarcinoma. Data of this type may merely reflect the aggressive biological behavior of most signet-ring cell tumors. Only one multivariate analysis has shown mucinous carcinoma to be a stage-independent predictor of adverse outcome, but the study was limited to tumors presenting with large bowel obstruction, which itself is an adverse prognostic factor.9§ By convention, signet-ring cell carcinomas, small cell carcinomas, and undifferentiated (histologic type) carcinomas are high grade. The only histologic types of colorectal carcinoma that have been shown to have adverse prognostic significance independent of stage are signet-ring cell carcinoma and small cell carcinoma.9 Nevertheless, signet-ring cell carcinoma may occur in hereditary nonpolyposis colon cancer syndrome in association with MSI-H.10 Thus, in cases of MSI-H signet-ring cell carcinoma, the prognostic significance may be determined by the molecular pathogenesis and may be favorable.∥ The term carcinoma, NOS (not otherwise specified) is not part of the World Health Organization classification.A number of grading systems have been suggested in the literature, but a single widely accepted and uniformly used standard for grading is lacking. Among the suggested grading schemes, the number of grades and the criteria for distinguishing among different grades vary markedly. In some systems, grades are defined on the basis of a single microscopic feature, such as the degree of gland formation, and in other systems, a large number of features are included in the evaluation. Irrespective of the complexity of the criteria, however, most systems stratify tumors into 3 or 4 grades as follows:Grade 1 Well differentiatedGrade 2 Moderately differentiatedGrade 3 Poorly differentiatedGrade 4 UndifferentiatedAppearance of individual histologic features may vary widely enough to make implementation of even the simplest grading systems problematic and, ultimately, subjective. Thus, a significant degree of interobserver variability in the grading of colorectal cancer has been shown to exist.9,11 Nevertheless, despite this variability, histologic grade has repeatedly been shown by multivariate analysis to be a stage-independent prognostic factor.9,12,13 Specifically, it has been demonstrated that high tumor grade is an adverse prognostic factor. In most studies documenting the prognostic power of tumor grade,9 the number of grades has been collapsed to produce a 2-tiered stratification for data analysis as follows:Low grade Well differentiated and moderately differentiatedHigh grade Poorly differentiated and undifferentiatedIn general practice, a 2-tiered grading system would also be expected to greatly reduce interobserver variability, since the widest variations in grading concern the stratification of low-grade tumors into well- or moderately differentiated categories. Pathologic identification of poorly differentiated or undifferentiated tumors is more consistent, and interobserver variability in diagnosing high-grade carcinoma is relatively small. Therefore, in light of its proven prognostic value, relative simplicity, and reproducibility, a 2-tiered grading system for colorectal carcinoma (ie, low grade and high grade) is recommended.6 The grading should be based on gland formation alone as follows6:Low grade ≥50% gland formationHigh grade 5 to 15 mm beyond the border of the muscularis propriapT3d Extensive invasion: >15 mm beyond the border of the muscularis propriaT4 Tumor directly invades other organs or structures§ (T4a) or perforates the visceral peritoneum∥ (T4b)* The designation T refers to the first resection of a primary tumor. The symbol pT refers to the pathologic classification of the TNM as opposed to the clinical classification. Pathologic classification is based on gross and microscopic examination. pT entails a resection of the primary tumor or biopsy sample adequate to evaluate the highest pT category; pN entails removal of nodes adequate to validate lymph node metastasis; and pM implies microscopic examination of distant lesions. Clinical classification (cTNM) is usually performed by the referring physician before treatment during initial evaluation of the patient or when pathologic classification is not possible and is typically based on information obtained by physical examination, serologic analyses, imaging studies, etc.1Tumor remaining in a patient after primary therapy (eg, surgical resection) is categorized by a system known as R classification.1,6,12 For example, this classification may be used by the surgeon to indicate the known or assumed status of the completeness of the surgical resection. For the pathologist, the R classification is relevant only to the margins of surgical resection specimens. That is, tumor involving the proximal, distal, or radial (circumferential) resection margin (see note K) on pathologic examination may be assumed to correspond to residual tumor in patient and classified as to whether the involvement is macroscopic or microscopic.6RX Presence of residual tumor cannot be assessedR0 No residual tumorR1 Microscopic residual tumorR2 Macroscopic residual tumorTumor remaining in a resection specimen following previous (neoadjuvant) treatment of any type (radiation therapy alone, chemotherapy therapy alone, or any combined modality treatment) is codified by the TNM using a prescript "y" to indicate the posttreatment status of the tumor (eg, ypT1).1,6 For many therapies, the classification of residual disease has been shown to be a strong predictor of postoperative outcome. In addition, the ypTNM classification provides a standardized framework for the collection of data needed to accurately evaluate new neoadjuvant therapies.Tumor that is locally recurrent after a documented disease-free interval following surgical resection is classified according to the TNM categories but modified with the prefix "r" (eg, rpT1). By convention, the recurrent tumor is topographically assigned to the proximal segment of the anastomosis unless that segment is small intestine.1,3† For colorectal carcinomas, carcinoma in situ (Tis) as a staging term includes cancer cells confined within the glandular basement membrane (intraepithelial carcinoma) or invasive into the mucosal lamina propria, up to but not through the muscularis mucosae (intramucosal carcinoma). This may be confusing because, in all other organ systems, the term carcinoma in situ is used to refer exclusively to malignant neoplasms that do not invade the underlying stroma. Therefore, for colorectal cancer, the terms intraepithelial carcinoma and intramucosal carcinoma are recommended as descriptive terms to subclassify pTis and to clarify the status of the tumor.5,6 Tumor extension through the muscularis mucosae into the submucosa is classified as T1. Some pathologists classify intraepithelial carcinoma as severe or high-grade dysplasia, especially in cases of inflammatory bowel disease.‡ The extent of perimuscular invasion has been reported to influence prognosis, regardless of whether regional lymph node metastasis is present. Thus, an optional expansion pT3 has been proposed.3 Extramural extension greater than 5 mm has been shown to be the critical subdivision associated with adverse outcome in most studies. Thus, a simpler subdivision, based on extension of 5 mm or less versus greater than 5 mm (ie, pT3a,b vs pT3c,d), may be justified.3 Extension of the tumor within lymphatics or veins does not count as local spread of tumor as defined by the T classification.3§ Direct invasion of other organs or structures includes invasion of other segments of colorectum by way of the serosa or mesocolon, for example, invasion of the sigmoid colon by carcinoma of the cecum. Intramural extension of tumor from one subsite (segment) of the large intestine into an adjacent subsite or into the ileum (eg, for a cecal carcinoma) or anal canal (eg, for a rectal carcinoma) does not affect the pT classification.3∥ Perforation of carcinoma through a peritonealized surface of the colon is classified as T4b.3 Subdivision of T4 into T4a and b is justified, because a number of large studies that have evaluated serosal penetration as an independent prognostic variable have demonstrated by multivariate analysis that it has a strong negative impact on prognosis.32–35 Specifically, it has been shown that the frequency of distant metastasis is higher in cases with perforation of the visceral peritoneum compared with cases with direct invasion of adjacent organs or structures without perforation of the visceral peritoneum (occurring in about 50% and 30% of cases, respectively).3 Furthermore, the median survival time following surgical resection for cure has been shown to be shorter for patients with pT4b tumors compared with those with pT4a tumors (with or without distant metastasis) as follows.3A study by Shepherd et al34 has suggested that the prognostic power of local peritoneal involvement in curative resections may supersede that of either local extent of tumor (T category) or regional lymph node status (N category). However, serosal penetration is often difficult to assess histopathologically and may be underdiagnosed. Documentation of peritoneal involvement by tumor demands meticulous pathologic analysis and may require extensive sampling and/or serial sectioning and can be missed on routine histopathologic examination. It has been shown that cytologic examination of serosal scrapings reveals malignant cells in as many as 26% of tumor specimens categorized as pT3 by histologic examination alone.34,36 In addition, the histopathologic findings associated with peritoneal penetration are heterogeneous, and standard guidelines for their diagnostic interpretation are lacking. Therefore, interobserver variability in the diagnosis of peritoneal penetration may be substantial, and since most pathologists tend to err on the side of conservative interpretation, underdiagnosis is likely for this reason as well.Shepherd et al34 analyzed the spectrum of microscopic features that may be seen with local peritoneal involvement by tumor and defined 3 types of local peritoneal involvement as follows:(1) A mesothelial inflammatory and/or hyperplastic reaction with tumor close to, but not at, the serosal surface(2) Tumor present at the serosal surface with inflammatory reaction, mesothelial and/or tumor cells on the serosal surface the with underlying of the visceral 3 types of local peritoneal involvement associated with tumor of the serosal no independent adverse on Therefore, the diagnosis of should these 3 types of serosal lymph nodes cannot be No regional lymph node in 1 to 3 lymph in 4 or more lymph The regional lymph nodes for the anatomic subsites of the large intestine are as right right middle right left inferior inferior superior rectal sigmoid left sigmoid inferior superior middle sigmoid inferior sacral superior middle inferior the sigmoid are pericolic and their involvement is classified as or according to the number lymph nodes include the sacral promontory middle rectal and inferior rectal in the or common nodes is classified as distant on of for Microscopic negative or lymph nodes are to be lymph nodes may be for microscopic of has been shown that negative lymph nodes for regional node Therefore, if than nodes are (ie, should be considered. If than nodes are after the use of this should be in the The should state the number of lymph nodes and the number involved by Data are to routine use of levels or microscopic examination of lymph nodes in large resection lymph nodes must be as regional versus according to the anatomic of the tumor. to lymph nodes is classified as distant metastasis and as by tumor greater than 3 mm in in the perirectal or without histologic evidence of residual lymph node in the is classified as regional node metastasis. However, a tumor less than or to 3 mm in is classified in the T as extension (ie, seen only in the should be as metastasis in a single lymph node for of regional lymph node metastasis is limited to the use of pathologic and histologic A of tumor in a single lymph node that is by routine histologic examination and mm or less may be defined as a The biological significance of disease single in a single within a single or involvement of as yet is studies, it is recommended that be classified as but reported with a note that the biological significance is The number of lymph nodes involved by should be biological significance of metastasis only by studies (eg, immunohistochemical or molecular is also at present. It is recommended that metastasis using studies alone also be reported with a note the significance of the findings in to histologically be classified as the data are to either the routine examination of levels of or the use of such as for and/or (eg, or reaction to tumor and Presence of distant metastasis cannot be No distant of organs is classified as studies, both invasion and invasion have been shown by multivariate analysis to be independent of The prognostic if of the anatomic of these structures is not Furthermore, it is not possible to from since both are Thus, the presence or of tumor invasion of should be reported in all cases and its anatomic within the invasion has been demonstrated by multivariate analysis to be an independent adverse prognostic of in has been shown to be an independent of unfavorable outcome and increased risk of of It has been shown that the of 5 or more of tumor the of invasion when it and to sampling significance of invasion is less because data specific to this are lacking. Nevertheless, it is recommended that the presence or of invasion and its anatomic should be reported in all reaction at the of invasive tumor and the presence of in the and or perirectal have both been shown in small studies to be independent favorable prognostic are associated with microsatellite instability and medullary and should be from Only and lymphocytes 4 or more should be of is If should be made between and growth of the tumor at the has been shown to have prognostic significance independent of stage and may Specifically, an of growth at the tumor border as opposed to a border is an adverse prognostic have been defined as of growth at the tumor has also been to as focal and tumor and defined as microscopic of undifferentiated cancer cells of the invasive front of the may be to the to the tumor with by should be in the macroscopic include the proximal, distal, and radial The radial margin represents the margin to the penetration of tumor. For all segments of the large intestine that are either colon, descending colon, sigmoid colon, upper or not by the radial margin is by of the or at radial margin has been demonstrated to be of in to risk of local recurrence after surgical resection of the rectal analysis has suggested that tumor involvement of the radial margin is the most critical in local recurrence in rectal For this reason, routine of the radial margin is suggested in all colorectal and of the from the tumor to the radial margin, the surgical the tumor is For segments of the colon that are by a peritonealized surface (eg, the only radial margin is the resection margin, and it is relevant when the of penetration of the tumor is on the of the colon and extends to this margin, with or without the serosal surface. For those tumors limited to an peritonealized of the the radial margin is not of its association with local involvement of the radial margin has for the primary tumor is serosal or (with serosal resection is only if all surgical margins are the radial That is, whether or not the tumor a serosal resection is if the resection margins distal, and do not tumor. If a radial margin is involved by therapy (eg, local may be to evaluate the proximal and distal resection margins can be obtained in 2 to the margin or to the on the of the tumor to the margin, the that best the status of the The from the tumor to the resection should be In cases of carcinoma arising in a of inflammatory bowel proximal and distal resection margins should be evaluated for and