Abstract PS4-11-08: Clinical characteristics and prognosis in interval detected breast cancer patients: a single institution cohort analysis

Abstract Aim: The aim of this study is to identify clinical characteristics and outcomes in a cohort of patients with interval-detected breast cancers. Methods: Interval-detected cancers were tumors that arose within a year of the last screening breast imaging that appeared normal, regardless of having a previous breast cancer diagnosis. Disease-free survival (DFS) was defined separately for primary and secondary cancers from the date of diagnosis of the interval tumor to the date of first recurrence or death. Results: We identified 43 patients who met the criteria for interval-detected breast cancer. Twelve patients had a previous diagnosis of breast cancer, 2 of whom had DCIS. Median follow-up was 24.2 mo ( 4.7-10.2.5). The median age of this cohort (second-primary interval cancer) was 49 (32-70); 10 (83.3%) were premenopausal. The mean time to the diagnosis of the new cancer was 28 months;14 mo for HER2 (+) and 38 mo for ER (+). The pathologic subtypes of invasive primaries were ER (+) in 6 and Her2 (+) in 4 (40%) patients. The interval tumor was detected in the ipsilateral breast in 8 patients, among whom 6 (75%) developed the second primary in the same localization of the primary tumor. Two of those (33%) had mastectomies as primary surgical treatment. There were 8 recurrences, among whom 5 were systemic and 4 were HER2 (+). Thirty-one patients had interval-detected primary breast cancers. The median follow up period was 25.4 mo (1-114.2). The median age was 51 (42-75) and 20 (64.5%) were premenopausal. Among them 2 were triple negative; 10 were Her2 (+); and 19 were ER (+). There were 7 recurrences; among whom 2 were systemic. In the whole cohort, 27 (62.8) patients had a family history of cancer. Among second-primary interval cancer patients, 8 of 12 patients had a family history. Among those 8 who had genetic testing, 5 had pathogenic variants (3:BRCA2; 1: PALB2;1:CHEK2)The DFS of the primary group and the secondary group were 96.8 (95% CI: 78,2-115.4) and 50.6 mo (95% CI: 35,1-98.6), respectively. There was a tendency for a worse outcome in the secondary interval cancer group (p:0.2), mostly driven by the HER2 subgroup. Conclusion: Interval cancers were associated with a high incidence of pre-menopausal status, family history or hereditary pathogenic variants. Secondary interval cancers were more likely to have HER2 (+) primary tumors, a shorter time to diagnosis of the interval cancer and a tendency to occur in the same site of the primary despite adequate local and systemic treatment. There was a tendency for a worse outcome in the secondary interval cancer group. Our data indicate closer follow-up for second primary interval cancers in HER2 (+) patients. These data should be interpreted with caution due to the retrospective nature; small sample size and should be validated in larger datasets. Citation Format: Y. Eralp, S. Bayrakceken, K. Turker Karayazi, G. Esen Icten, F. Tokat, N. Bese, T. Korkmaz, O. Sonmez, H. Kara, N. Bakir, C. Uras. Clinical characteristics and prognosis in interval detected breast cancer patients: a single institution cohort analysis [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-11-08.