Abstract P1-08-11: Incidence and Factors Predicting Survival in Inflammatory Breast Cancer: An Updated SEER Analysis

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Abstract Introduction: Inflammatory breast cancer (IBC) is an aggressive type of breast cancer (BC) accounting for 1-5% of all BC cases and contributes to 8-10% of BC deaths. IBC is usually diagnosed at locally advanced or metastatic stage. It occurs more frequently in younger women, although the exact incidence is unknown. We examined the overall incidence of IBC from 2010 -2021, the age-adjusted incidence among those younger than 40 years and incidence among different racial groups. Additionally, we evaluated the factors predicting overall survival (OS) in IBC patients diagnosed between 2010-2021. Method: We identified patients diagnosed with IBC from 2010 – 2021 using Surveillance, Epidemiology, and End Results (SEER) database and examined the incidence rate (IR) per 1000,000 in overall population, age-adjusted IR for those< 40 years (y), and IR by race: White, Black, Asian/Pacific Islander (API), American Indian/Alaska Native (AI/AN). Data on baseline demographic (age, gender, race), clinicopathologic (clinical TNM stage, grade, tumor subtypes) and treatment characteristics (chemotherapy (CT), radiation therapy (RT), surgery (Sx)) were abstracted. Frequencies of IBC subtypes were summarized by hormonal status: hormone receptor positive (HR+), HER2+, triple negative IBC (TNBC). Univariate and multivariate cox-proportional hazard regression was conducted to analyze the factors predicting survival in IBC. Results: A total of 1245 patients were included, the majority 99.8% (n=1422) were females, and 71% (n=1014) White, 18% (n=258) Black, 10% (n=135) API, and 1% (n=16) AI/AN. The median age at diagnosis of the cohort was 60 y (range: 20-85 y). 32% were diagnosed with HR+/HER2-, 22% with TNBC, 16% with HR-/HER2+, and 16% HR+/HER2+ IBC. The IR of IBC has decreased over the years, from 2.1 per 1000,000 in 2010 to a most recent IR of 1.3 in 2021. Age-adjusted IR also decreased, where people less than 40 y had an age-adjusted IR of 0.5 in 2010, and a most recent IR of 0.3 in 2021. When analyzing IBC IR trends by race, we found a decreasing trend among all racial groups, except for AI/AN where we found a variable trend with initial decline until 2014 followed by steady increase in IR with peak value of 1.2 in 2021. The overall IBC IR in 2021 was 1.2 among Blacks and AI/AN, 1 among White, and 0.5 among API. Notably, in younger patients (<40 y), Black and AI/AN had the highest age-adjusted IR of 0.5 and 0.6 respectively in 2021. Multivariate analysis showed that patients diagnosed with IBC at age younger than 60 y (median age of study cohort) had a worse OS than those diagnosed at an age older than 60 y (HR 1.18, 95%CI: 1.02-1.38, P= 0.02). Compared to White, Black patients had worse OS (HR 1.13, 95%CI: 1.09-1.58, P= 0.004), While AI/AN patients had a better OS (HR 0.30, 95%CI: 0.09-0.94, P=0.03). Compared with TNBC subtype, non-TNBC tumors were associated with improved OS. [HR-/HER2+ (HR 0.43, 95%CI:0.34-0.55, P=0.00), HR+/HER2- (HR=0.48, 95%CI:0.40-0.58, P=0.00), and HR+/HER2+ (HR 0.37, 95%CI: 0.29-0.47, P= 0.00)]. Moreover, patients who were treated with CT (HR 0.50, 95%CI: 0.41-0.61, P=0.00) and Sx (HR 0.58, 95%CI: 0.33-0.48, P=0.00) had better OS than those who did not. Interestingly, no significant association was noted between survival and receipt of RT (HR 0.89, 95%CI: 0.74-1.06, P=0.20). Conclusion: The incidence of IBC has decreased over the past decade. Black women regardless of their age and AI/AN younger continue to have a higher incidence of IBC. The prognosis of IBC remains poor, especially among Black, those diagnosed at age younger than 60 y and TNBC subtype. Chemotherapy and surgery seem to improve OS in IBC. Larger studies are needed to explore the potential risk factors for IBC among different races. Citation Format: Malak Alharbi, Jayasree Krishnan, Kriti Ahuja, Mengyu Fang, Han Yau, Zunariah Shah, Riya Patel, Arya M. Roy, Shipra Gandhi. Incidence and Factors Predicting Survival in Inflammatory Breast Cancer: An Updated SEER Analysis [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P1-08-11.

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