Importance: Breast cancer in young women has a less favorable prognosis compared with older women. Yet, comprehensive data on recent trends and how period and cohort effects may affect these trends among young women are not well-known.Objective: To evaluate breast cancer incidence among young women in the US over a 20-year period by race and ethnicity, hormone receptor status (estrogen receptor [ER] and progesterone receptor [PR]), tumor stage, and age at diagnosis, as well as how period and cohort effects may affect these trends.Design, Setting, and Participants: This cross-sectional study used data from Surveillance, Epidemiology, and End Results 17 registries (2000-2019). Women aged 20 to 49 years with a primary invasive breast cancer were included. Data were analyzed between February and June 2023.Main Outcomes and Measures: Age-standardized incidence rates (ASIR), incidence rate ratios (IRR), and average annual percent changes (AAPC) stratified by race and ethnicity, hormone receptor status, tumor stage, and age at diagnosis.Results: Out of 217 815 eligible women (1485 American Indian or Alaska Native [0.7%], 25 210 Asian or Pacific Islander [11.6%], 27 112 non-Hispanic Black [12.4%], 37 048 Hispanic [17.0%], 126 960 non-Hispanic White [58.3%]), the majority were diagnosed with an ER+/PR+ tumor (134 024 [61.5%]) and were diagnosed with a stage I tumor (81 793 [37.6%]). Overall, invasive breast cancer incidence increased (AAPC, 0.79; 95% CI, 0.42 to 1.15), with increasing trends across almost all racial and ethnic groups. ASIR increased for ER+/PR+ (AAPC, 2.72; 95% CI, 2.34 to 3.12) and ER+/PR− tumors (AAPC, 1.43; 95% CI, 1.00 to 1.87), and decreased for ER−/PR+ (AAPC, −3.25; 95% CI, −4.41 to −2.07) and ER−/PR− tumors (AAPC, −0.55; 95% CI, −1.68 to 0.60). For women aged 20 to 29 and 30 to 39 years, ASIRs were highest among non-Hispanic Black women (age 20-29 years: IRR, 1.53; 95% CI, 1.43 to 1.65; age 30-39 years: IRR, 1.15; 95% CI, 1.12 to 1.18). For women aged 40 to 49 years, ASIR was lower for non-Hispanic Black women (IRR, 0.96; 95% CI, 0.94 to 0.97) compared with non-Hispanic White women. Incidence rates increased for stages I and IV tumors but decreased for stage II and III tumors. Age-period-cohort analysis demonstrated both cohort and period effects on breast cancer incidence (P < .001).Conclusions and Relevance: In this population-based cross-sectional analysis, an increase in breast cancer incidence rates among young US women and age-related crossover between non-Hispanic White and Black women were observed. Prevention efforts in young women need to adopt a targeted approach to address racial disparities in incidence rates observed at different age phases.

OBJECTIVE: To examine the associations of maternal and child characteristics with early pregnancy maternal concentrations of testosterone, androstenedione, progesterone, 17-hydroxyprogesterone, and estradiol (E2). METHODS: We analyzed these hormones among 1,343 women with singleton pregnancies who donated serum samples to the Finnish Maternity Cohort from 1986 to 2006 during the first half of pregnancy (median 11 weeks). The associations of maternal and child characteristics with hormone concentrations were investigated by correlation and multivariable regression. RESULTS: Women older than age 30 years had lower androgen and E2 but higher progesterone concentrations than women younger than that age. Multiparous women had 14% lower testosterone, 11% lower androstenedione and 17-hydroxyprogesterone, 9% lower progesterone, and 16% lower E2 concentrations compared with nulliparous women (all P<.05). Smoking mothers had 11%, 18%, and 8% higher testosterone, androstenedione, and 17-hydroxyprogesterone levels, respectively, but 10% lower progesterone compared with nonsmoking women (all P<.05). E2 concentrations were 9% higher (P<.05) among women with a female fetus compared with those with a male fetus. CONCLUSION: Parity, smoking, and, to a lesser extent, maternal age and child sex are associated with sex steroid levels during the first half of a singleton pregnancy. The effects of smoking on the maternal hormonal environment and the possible long-term deleterious consequences on the fetus deserve further evaluation. LEVEL OF EVIDENCE: II

Background: Excess body weight and a sedentary lifestyle are associated with the development of several diseases, including cardiovascular disease, diabetes and cancer in women. One proposed mechanism linking obesity to chronic diseases is an alteration in adipose‐derived adiponectin and leptin levels. We investigated the effects of 12‐month reduced calorie, weight loss and exercise interventions on adiponectin and leptin concentrations.Methods: Overweight/obese postmenopausal women (n = 439) were randomized as follows: (i) a reduced calorie, weight‐loss diet (diet; N = 118), (ii) moderate‐to‐vigorous intensity aerobic exercise (exercise; N = 117), (iii) a combination of a reduced calorie, weight‐loss diet and moderate‐to‐vigorous intensity aerobic exercise (diet + exercise; N = 117), and (iv) control (N = 87). The reduced calorie diet had a 10% weight‐loss goal. The exercise intervention consisted of 45 min of moderate‐to‐vigorous aerobic activity 5 days per week. Adiponectin and leptin levels were measured at baseline and after 12 months of intervention using a radioimmunoassay.Results: Adiponectin increased by 9.5% in the diet group and 6.6% in the diet + exercise group (both P ≤ 0.0001 vs. control). Compared with controls, leptin decreased with all interventions (diet + exercise, −40.1%, P < 0.0001; diet, −27.1%, P < 0.0001; exercise, −12.7%, P = 0.005). The results were not influenced by the baseline body mass index (BMI). The degree of weight loss was inversely associated with concentrations of adiponectin (diet, P‐trend = 0.0002; diet + exercise, P‐trend = 0.0005) and directly associated with leptin (diet, P‐trend < 0.0001; diet + exercise, P‐trend < 0.0001).Conclusion: Weight loss through diet or diet + exercise increased adiponectin concentrations. Leptin concentrations decreased in all of the intervention groups, but the greatest reduction occurred with diet + exercise. Weight loss and exercise exerted some beneficial effects on chronic diseases via effects on adiponectin and leptin.

Knowledge of the stability of serum samples stored in large biobanks is pivotal for reliable assessment of hormone-dependent disease risks. We studied the effects of sample storage time and season of serum sampling on the stability of 25-hydroxy vitamin D (25-OHD) and androstenedione in a stratified random sample of 402 women, using paired sera from the Finnish Maternity Cohort. Serum samples selected were donated between 6 and 24 yr ago. The storage time did not affect serum 25-OHD and androstenedione levels. However, there was a significant mean difference in the 25-OHD levels of sera withdrawn during winter (first sample) vs. during summer (second sample; –18.4 nmol/l, P ≤ 0.001). Also at the individual level, there were significant differences in average 25-OHD levels between individuals with the paired sera taken at winter–winter compared with other alternatives (summer–winter, winter–summer, and summer–summer). The androstenedione levels showed no such differences. Long-term storage does not affect serum 25-OHD and androstenedione levels, but sampling season is an important determinant of 25-OHD levels. Stored serum samples can be used to study disease associations with both hormones. However, sampling season needs to be taken into account for 25-OHD by considering matching and stratification and, if possible, serial sampling.

Importance: Menopausal hormone therapy (MHT) is the treatment of choice for symptoms of menopause. However, its adoption is hindered by the risk-benefit trade-off in relation to acute and chronic diseases.Objective: To evaluate trends in and correlates of MHT use among postmenopausal women in the US from 1999 to March 2020.Design, Setting, and Participants: This serial cross-sectional analysis of MHT use used data from the nationally representative National Health and Nutrition Examination Survey (NHANES). Participants included noninstitutionalized US postmenopausal women from 10 NHANES study cycles (1999-2000 to 2017-March 2020 [pre–COVID-19 pandemic]). Data were analyzed from December 2023 to April 2024.Exposures: NHANES study cycle.Main Outcomes and Measures: Prevalence of MHT use was extracted from the prescription medication data collected during NHANES household interviews. MHT formulations were determined by hormone type.Results: Data on 13 048 US postmenopausal women (47.1% ≥65 years old) were analyzed. From 1999 to 2020, the prevalence of MHT use decreased among women of all age groups, from 26.9% (95% CI, 22.6%-31.7%) in 1999 to 4.7% (95% CI, 3.4%-6.5%) in 2020. Until 2002, MHT use was highest among women aged 52 to 65 years, but since 2005, MHT use has been highest among women younger than 52 years. MHT use decreased by 23.5% (95% CI, 11.4%-35.6%), 31.4% (95% CI, 23.4%-39.5%), and 10.6% (95% CI, 6.3%-14.8%) for women younger than 52 years, 52 years to younger than 65 years, and 65 years and older, respectively. Prevalence of MHT use decreased from 13.8% (95% CI, 8.5%-21.7%) to 2.6% (95% CI, 1.5%-4.6%) for Hispanic women, 11.9% (95% CI, 8.5%-16.3%) to 0.5% (95% CI, 0.2%-1.1%) for non-Hispanic Black women, and 31.4% (95% CI, 27.1%-36.1%) to 5.8% (95% CI, 4.1%-8.2%) for non-Hispanic White women. Non-Hispanic White women consistently had the highest prevalence of MHT use. Estrogen-only formulation accounted for more than 50% of the MHT for most study periods. The prevalence of MHT use varied by family income-to-poverty ratio, health insurance coverage in all racial and ethnic groups, weight, and smoking status among non-Hispanic White women, as well as by education attainment among non-Hispanic Black and Hispanic women.Conclusions and Relevance: Results of this cross-sectional study show that over the past 2 decades, MHT use declined among US postmenopausal women of all age and racial and ethnic groups. Women of racial and ethnic minority groups had lower prevalence of MHT use compared to non-Hispanic White women.