Digital breast tomosynthesis and breast cancer detection in older women: Smaller tumors and more invasive lobular carcinomas.

285 Background: Digital breast tomosynthesis (DBT) has shown improved breast cancer detection over digital mammography (DM) in trials of women aged 46-69. However, its benefit of early detection for older women and its effectiveness in detecting more difficult-to-detect invasive lobular carcinomas (ILCs) remain uncertain. We hypothesized that, among women aged ≥67, DBT may detect tumors at smaller sizes and detect more ILCs compared to DM, and that these benefits would extend to women aged ≥75. We also hypothesized that DBT would detect ILCs at smaller sizes than DM. Methods: This was a retrospective SEER-Medicare cohort study of women aged ≥67 diagnosed with screen-detected ER+/HER2- breast cancer between 2015 to 2019. Screen-detected cases were identified using a validated claims-based algorithm. The primary exposure was screening modality (. The primary and secondary outcomes were tumor size at diagnosis (categorized in 10-mm intervals from 0–10 to ≥51 mm) and histology (ILC vs. other histology), respectively, and their associations with screening modality were assessed using ordinal and multivariable logistic regression. An interaction term was included to evaluate whether DBT is associated with detecting ILCs at smaller sizes. Results: Among 12,582 women, half (49.2%) received DBT at cancer detection. The majority were non-Hispanic White (82.4%), not dual eligible for Medicare and Medicaid (89.5%), and between ages 67 and 75 (55.8%). Among DBT-detected cases, 41.2% of tumors were ≤10 mm, compared to 37.8% among DM-detected cases (P < 0.001). multivariable analyses, DBT was associated with 9% higher odds of detecting smaller tumors compared to DM (aOR: 1.09, CI: 1.01-1.17), but this association was not observed in women aged ≥75 (aOR: 1.01, CI: 0.91-1.13). DBT was also associated with 25% higher odds of detecting ILC compared to DM (aOR: 1.25, 95% CI: 1.12–1.39), and this association persisted among women aged ≥75 (aOR: 1.22; CI: 1.04–1.43). No significant interaction was observed between screening modality and tumor histology on tumor size. Conclusions: Our findings support the use of DBT as a routine screening modality for women aged 67-74 to improve the detection of ILCs. However, DBT did not demonstrate a significant advantage over DM in detecting smaller tumors among women aged ≥75, nor did it detect ILCs at smaller tumor sizes, which suggests that it may not facilitate earlier detection in this age group.