Clinical characteristics of interval breast cancer within 12 months and 13-24 months in Utah.
Authors: Wei Mei , Pappas Lisa , Van Meter Margaret Elizabeth McCormick , Freer Phoebe , Buys Saundra S. , Curtin Karen 
Published: June 2023

10531 Background: A breast cancer (BC) that emerges following a negative/benign screening mammogram (SMG) but before the next expected SMG is referred to as an interval breast cancer (IBC). Current guidelines vary in the recommended frequency of SMG: some guidelines support SMG every 12 months, others every 24 months, and many adapt the 12- or 24-month recommendation by age. This study compared the clinical characteristics of IBC that developed within a 3-12 month interval (12m IBC) and a 13-24 month interval (24m IBC) in a statewide population. Methods: This is a retrospective cohort study using demographic/medical records in the Utah Population Database linked to the Utah Cancer Registry, a Surveillance, Epidemiology, and End Results (SEER) registry. Index SMG refers to the SMG just prior to a diagnostic mammogram or other clinical encounter, which led to a BC diagnosis before the next, expected SMG. Women ages ≥38y who underwent SMG during 2005-2019 at Intermountain Healthcare and University of Utah Health, had no history of BC prior to first SMG, and had BI-RADS assessment of normal or benign finding at index SMG were included. Clinical characteristics of 12m IBC and 24m IBC were compared using multivariable logistic regression to provide odds ratio estimates with covariate adjustment for age at diagnosis, stage, tumor size, grade, histology, biomarkers, breast density, body mass index, family history of breast cancer, and age at first birth. Women who developed IBC during the 3-12 month interval were not counted in the 24m IBC group. Results: A total of 7776 BC were observed in this study, among which 2122 were IBC; 486 (6.3%) 12m IBC and 1636 (21.0%) 24m IBC. Women with 12m IBC and 24m IBC had similar rates of a first-degree family history of breast cancer (16% and 17%, respectively). Women 70 and older were the least likely to develop IBC in 12 months as compared to 24 months (OR 2.34, 95% CI: 1.61-3.40, p< 0.01). The odds of having axillary lymph node metastases (regional disease) at the time of BC diagnosis was higher among 12m IBC than 24m IBC (OR 1.68, 95% CI: 1.29-2.19, p< 0.01). A total of 41 women with IBC had distant metastatic disease at the time of diagnosis (5% 12m IBC, 1% 24m IBC). Among those, the odds that metastatic IBC would be a 12m IBC were significantly higher than 24m IBC (OR = 4.07, CI 2.03-8.29, p< 0.01). The 12m IBC group was more likely to be HER2 positive (OR 2.10, 95% CI: 1.36-3.22, p< 0.01) or triple negative (OR 2.08, 95% CI: 1.26-3.39, p< 0.01) than the 24m IBC group. Extremely dense breast tissue at SMG increased the odds of developing 12m IBC compared to 24m IBC (OR 2.05, 95% CI: 1.13-3.80, p< 0.01). Conclusions: Compared to 24m IBC, 12m IBC appeared to be more advanced and aggressive. Women with Extremely dense breast tissue were more likely to develop 12m IBC than 24m IBC. These results suggest that women with extremely dense breast tissue or age < 70y may benefit from annual SMG instead of biennial SMG.