10585 Background: Prior studies suggest that thyroid cancer (TC) survivors may have an elevated risk of secondary malignancies. However, whether this risk differs by TC histology, specifically with breast cancer (BC), remains unclear. We aimed to investigate the association between TC subtype—papillary thyroid carcinoma (PTC) versus medullary thyroid carcinoma (MTC)—and subsequent BC risk, adjusting for demographic factors. Methods: We conducted a retrospective cohort study using the SEER (2000–2022), including adults with a primary, microscopically confirmed PTC or MTC. Subsequent BC occurrence was defined as a binary outcome (yes/no). Multivariable logistic regression was used to estimate adjusted odds ratios (aORs) for MTC versus PTC, controlling for age (<50 vs ≥50 years), sex, and race. Stratified analyses by age and race were also performed. Stata 15 was used for statistical analyses. Results: 14,840 patients (14,563 PTC, 277 MTC) were included. MTC patients were older (mean 59.08±12.66 vs 56.16±12.98 years, p<0.001) and had a higher proportion of males (44.4% vs 29.4%, p<0.001). The overall incidence of secondary BC was lower in MTC patients (7.6% vs 22.5%, p<0.001). In unadjusted logistic regression, MTC was associated with significantly lower BC risk (OR=0.28, 95% CI: 0.18–0.44, p<0.001). After adjustment, MTC remained significantly protective (aOR=0.34, 95% CI: 0.22–0.55, p<0.001). Stratified analyses demonstrated consistent findings across age groups (<50: aOR=0.10, 95% CI: 0.03–0.42; ≥50: aOR=0.34, 95% CI: 0.21–0.54), , as well as white and Hispanic patients. Conclusions: Survivors of MTC have a substantially lower risk of developing secondary BC compared to PTC survivors. This association persists after adjustment for age, sex, and race, and is consistent across age and most racial subgroups. However, different BC types were not assessed due to limited number of BC patients among MTC survivors, and the small MTC sample size and potential survival differences between groups may affect the results. These findings highlight a possible effect of TC subtype on BC risk, suggesting the potential influence of underlying biological or genetic mechanisms. Baseline demographic characteristics of patients with papillary and medullary thyroid carcinoma. Characteristic Papillary Thyroid Carcinoma (PTC) (N=14,563) Medullary Thyroid Carcinoma (MTC) (N=277) P-value Age at Diagnosis 0.0002* Mean ± SD, years 56.16 ± 12.98 59.08 ± 12.66 Median, years 57 61 Sex, n (%) <0.001† Female 10,288 (70.6) 154 (55.6) Male 4,275 (29.4) 123 (44.4) Race, n (%) 0.015† White 10,263 (70.5) 197 (71.1) Black 921 (6.3) 15 (5.4) American Indian 77 (0.5) 1 (0.4) Asian 1,379 (9.5) 13 (4.7) Hispanic 1,903 (13.1) 50 (18.1) SD: Standard Deviation. *P-value from two-sample t-test (equal variances assumed). †P-value from chi-square test for the overall distribution across categories.
Liu et al. (Wed,) studied this question.