Outcomes of very young women and adolescent (VYWAA) with breast cancer (BC) in rural and urban Saskatchewan: A population-based cohort study.

1571 Background: BC is uncommon in VYWAA (≤ 35 years) and accounts for about 1.8% of all BC. As BC screening is typically recommended for women aged 50-74 years there is a risk of delayed diagnosis of BC in VYWAA especially those with rural residence. The current study aims to assess outcomes of a cohort of VYWAA with BC in relation to their place of residence in the province of Saskatchewan over a period of 20 years. Methods: In this population-based retrospective cohort study all women ≤ 35 years with histologically documented epithelial BC during 2000-2019 were evaluated. Survival of the entire cohort and its subgroups was estimated using the Kaplan−Meier method, and the survival distribution of different groups was compared by the log rank test. A multivariate Cox proportional hazard model was performed. Various clinical and demographic variables were examined for their prognostic importance of overall survival (OS) for all stages and disease-free survival (DFS) for early-stage BC. Results: 248 eligible women with a median age of 32 years were identified, 24% were <30 years of age. Of all patients, 51% had node positive disease, 7% had DCIS, 15% stage I, 42% stage II, 22% stage III and 11% had stage IV disease at initial presentation. Among them 42% had hormone receptor +, 28% had HER2 + and 23% had triple negative BC (TNBC).16% developed BC within 1-year of pregnancy. 53% were rural resident and 47% were urban resident. Significant differences were noted between the two groups regarding smoking history (42 vs. 25%), HER2+BC (35% vs. 20%) and mean platelet count (285 vs. 258). Median follow up for all women was 91 months with a total follow up period of 294 months. Median DFS of VYWAA with stage I to III disease has not reached. 10-year estimated DFS of all women was 66%. 10-year DFS for stage I and II was 73% and 75%, respectively, vs. 43% for stage III (p<0.001). Median OS of entire cohort with stage 0-IV BC has not reached. 10-year OS of all VYWAA was 69%. 10 years OS of urban women was 79% compared to 65% for rural resident (p=0.041). 10-year OS of women age >30 years was 74% compared to 62% for age 26-30 years and 55% for age <26 (p=0.35).10 years OS of VYWAA with non-TNBC was 73% compared to 63% for with TNBC (p=0.028). On multivariate analysis for women with early-stage disease, stage III BC, HR, 3.0 (1.80-4.92) and grade III BC were significantly correlated with inferior DFS. On a multivariate analysis for OS of all VYWAA with stage 0 to IV disease, rural residence, HR, 1.75 (1.08-2.81); TNBC, HR, 2.25 (1.34-3.80), and stage IV disease, HR, 8.1 (4.72-13.94) were correlated with inferior OS. Conclusions: Very young women and adolescent with BC have a high incidence of node-positive disease and HER2+ and TNBC subtypes. TNBC and grade III disease were associated with inferior DFS in stage I-III disease whereas stage IV BC, TNBC and rural residence were correlated with inferior survival in women with stage 0-IV disease.

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