Biological Subtypes and Risk of Second Primary Breast Cancer in Inflammatory Breast Cancer – Population Based Analysis from the California Cancer Registry.

Abstract

Abstract Background: Inflammatory breast cancer (IBC) is a rare and aggressive form of breast cancer. Our group's recent study revealed that the 5-year breast cancer specific survival for IBC is 49%, an improved rate compared to historical studies (∼ 30%). This could be attributed to evolution in modern modalities of treatment including utility of transtuzumab. Given marginally improved survival, these women are also at risk for second breast cancers. Here we investigate the risk of second breast cancer in IBC compared to the general population.Methods: We identified 75,039 IBC, LABC and non-T4 female breast cancer cases in the California Cancer Registry during the period of 1999-2005. We excluded synchronous tumors (cancer diagnosed <6 months from first breast cancer diagnosis). Standardized incidence ratio (SIR) with 95% CI is used to calculate the risk of second breast cancer by comparison to underlying general population.Results: A total of 1488 second breast cancer patients were identified, including 60 with a first diagnosis of IBC, 26 with a first diagnosis of LABC, and 1402 with a first diagnosis of non T-4 breast cancer. The risk of second breast cancer in IBC compared to the underlying population at risk was observed to be highest in IBC [SIR= 4.12 (3.14-5.30)] followed by LABC [SIR= 1.95 (1.28-2.86)], and non-T4 [SIR= 1.16 (1.10-1.23)] cases. Patients with IBC were more likely to be [HR-/HER2+] (43.8%) compared to LABC (33.3%) and non-T4 (8.7%) [p=<0.0001]. IBC and LABC were also increasingly associated with contralateral breast cancer (96%).Table-1: Risk of second breast cancer compared to general population by classification of first breast cancer Cohort sizeObserved 2nd breast cancerExpected 2nd breast cancerSIR (95%CI)IBC14746014.574.12 (3.14-5.30)LABC11032613.321.95 (1.28-2.86)Non-T472,46214021205.851.16 (1.10-1.23) Table-2: Hormone Receptor/Her2-neu status, subtype, laterality of second breast cancer by classification of first breast cancer £Receptor status of the first tumor*IBCLABCNon-T4TotalHR+/Her2+147(17%)123(20%)6405(15.5%)6675(15.7%)HR-/Her2+217(25%)98(16%)2713(6.6%)3028(7.1%)HR+/Her2-318(36.5%)268(43.8%)26,680(65%)27,266(64%)HR-/Her2-187(21.5%)124(20.2%)5303(12.9%)5614(13.2%)Receptor status of the second tumor** HR+/Her2+2 (6.2%)4 (26.7%)97 (12.6%)103 (12.6%)HR-/Her2+14 (43.8%)5 (33.3%)67 (8.7%)86 (10.5%)HR+/Her2-11 (34.4%)6 (40%)468 (60.6%)485 (59.2%)HR-/Her2-5 (15.6%)0 (0%)140 (18.1%)145 (17.7%)Subtypes of the 2nd primary breast tumor*** OtherIBC11(18.3%)2(5%)13(21.7%)33(55%)LABC5(19%)1(4%)11(42.4%)9(34.6%)Non-T425(1.8%)8(0.5%)482(34.4%)887(63.2%)Contralateral Breast cancer58(96.6%)25(96.1%)1165(83%)1484£ p value <0.0001 for all comparisons, *43% of data missing;** 49% of data missing;*** 8% of data missing.Conclusions: HR-/HER2+ biologic subtype of IBC was increasingly associated with development of second breast cancers and majority of them (96%) involved the contralateral breast with possible implications for IBC treatment. Among the investigated breast cancer subtypes IBC was associated with the highest risk of second breast cancers compared to the underlying population reinforcing IBC as an unique biologic entity. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2056.