Abstract B037: Early-Onset Cancer: A Focus on Pregnancy-Associated Cases

Abstract Background: Recent data in the U. S. show a rising rate of early-onset cancers (diagnosed before age 50) over the past decade, with the largest increase in rates seen in the 30-39 age group and the highest number of cases in the 40-49 age group. Simultaneously, the maternal age at the time of pregnancy has increased, with 38% of first births now occurring in women aged 30 and older. The increasing incidence of early-onset cancer, coupled with increasing maternal age, could result in more cancers diagnosed during pregnancy or postpartum. The present study describes trends in the incidence of cancer during pregnancy and postpartum and identifies predictors of pregnancy-associated cancers. Methods: We identified cancer cases diagnosed in adults from 2015 to 2023 with at least one health encounter in the time frame in a large health system in the greater Los Angeles area. We identified patients with obstetric International Classification of Diseases (ICD-10) codes and/or oncology notes mentioning pregnancy in the two years before and six months following the patient’s date of cancer diagnosis. Pregnancy-associated cancer was defined as a diagnosis during pregnancy or within two years postpartum (following any birth, miscarriage, or ectopic pregnancy). Descriptive statistics characterized demographic and cancer-related factors. Results: Among 40, 432 patients with cancer during the study period, we identified 217 pregnancy-associated cancers in 216 patients one individual had thyroid cancer diagnosed following a pregnancy, and breast cancer in a subsequent pregnancy. Median age at cancer diagnosis was 37 (range: 24-50). 13% of patients were Asian, 6% were Black or African American, 15% were Hispanic, and 56% were non-Hispanic White. The majority (n=193, 92%) of pregnancy-associated cancers were solid tumors (vs. 8% hematological), of which the most common sites were breast (N=85, 44%), thyroid (N=35, 18%), cervix (N=13, 7%), central nervous system (N=11, 6%), ovarian (N=8, 4%) and colon (N=6, 3%). Most solid tumors were diagnosed at early stages (50% stage I, 21% stage II vs. 11% stage III, 9% stage IV), with 15 in situ cancers diagnosed (6 breast cancer, 6 gynecologic malignancies, and 3 melanoma). 60 cancers were diagnosed during pregnancy (33% breast and 13% thyroid cancer), 91 during one year postpartum (32% breast and 20% thyroid cancer), and 66 between one and two years postpartum (55% breast and 14% thyroid cancer). Analyses of the total incidence of and predictors of pregnancy-associated cancer are ongoing. Conclusions: Pregnancy-related cancers present challenges for maternal-fetal care and oncology. The two-year interval postpartum may represent a key window for surveillance and earlier diagnosis. Identifying predictors, treatment patterns, and risk factors for adverse outcomes will help develop screening strategies to diagnose pregnancy-related cancer early and improve clinical management of these cases. Citation Format: Nicole C. Loroña, Jenny Harris, Jane C. Figueiredo. Early-Onset Cancer: A Focus on Pregnancy-Associated Cases abstract. In: Proceedings of the AACR Special Conference in Cancer Research: The Rise in Early-Onset Cancers—Knowledge Gaps and Research Opportunities; 2025 Dec 10-13; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2025;31 (23Suppl): Abstract nr B037.