ImportanceBreast cancer (BC) is commonly diagnosed among Caribbean women. Shifts in reproductive patterns modify the incidence of BC diagnosis and age at BC diagnosis in population-based studies; however, reproductive patterns in Caribbean women remain understudied.ObjectiveTo describe the temporal trends in reproductive patterns and age at BC diagnosis in Caribbean-born women.Design, Setting, and ParticipantsA cross-sectional observational study—the Caribbean Women’s Cancer Study—was conducted, with data on reproductive patterns known to affect BC risk collected in The Bahamas, Barbados, Cayman Islands, Dominica, Haiti, Jamaica, and Trinidad and Tobago. Participants were recruited prospectively. The sample included women born in Caribbean countries and diagnosed with invasive BC and/or ovarian cancer from June 1, 2010, to June 30, 2018, and was divided into 4 birth cohorts (born before 1950, 1950-1959, 1960-1969, and in or after 1970). Data were analyzed between August 1, 2023, and July 31, 2024.ExposuresReceipt of a BC diagnosis and birth in a Caribbean country.Main Outcomes and MeasuresChange in reproductive patterns between birth cohorts, including age at BC diagnosis, family history of cancer, age at first pregnancy, number of pregnancies, number of full-term pregnancies, number of siblings, age at menarche and menopause, estrogen receptor status, and germline pathogenic/likely pathogenic variants.ResultsOf 1015 participants diagnosed with BC and ovarian cancer, 995 women (mean [SD] age, 46.6 [10.8] years; 605 [81.8%] Afro-Caribbean, 98 [13.2%] East Indian, 22 [3.0%] White, and 12 [1.6%] >1 race) received a diagnosis of invasive BC. Comparison from older to younger birth cohorts (presented in the order of born before 1950, 1950-1959, 1960-1969 and in or after 1970) showed an increased proportion of women experiencing menarche at age 12 years or younger (33.0% vs 47.3% vs 45.5% vs 57.9%; P < .001), women with no pregnancies (6.8% vs 6.8% vs 10.5% vs 22.8%; P < .001), and nulliparous women (8.6% vs 9.2% vs 13.9% vs 27.6%; P < .001). Younger age at BC diagnosis was observed in women experiencing menarche at age 12 years or younger (mean [SD], 45.0 [10.5] years) vs 15 years or older (mean [SD], 49.1 [11.2] years) and in nulliparous women (mean [SD], 42.1 [11.2] years) vs 3 or more full-term pregnancies (mean [SD], 49.9 [10.6] years; P < .001). For every year of first pregnancy delay, women had a 4% increased chance of being diagnosed with estrogen receptor–positive tumors (odds ratio, 1.04; 95% CI, 1.01-1.08; P = .02).Conclusions and RelevanceIn this cross-sectional study, between each 10-year birth cohort, women diagnosed with BC had a lower age at menarche, number of pregnancies, and number of full-term pregnancies. These findings suggest that interventions targeting other BC risk factors need to be implemented.
