No abstract

Background: Bone is the most common site of metastasis in metastatic breast cancer patients. Notably, bone biopsy is considered technically challenging with concerns regarding yield and reproducibility of immunohistochemistry technique. Our goal was to assess tumor subtype concordance between breast and bone biopsies done in patients with bone only metastases. Methods: We identified patients followed at MD Anderson Cancer Center for at least 6 months from 01/01/1997 to 12/31/2015 with bone as first site of metastasis. Breast and bone biopsy immunohistochemistry was used to categorize tumor subtype with hormone receptor positive (HR+) defined as ER or PR >1%. The following four tumor subtypes were identified: luminal A-like (HR+, HER2-), luminal B-like (HR+, HER2+), triple negative (HR-, HER2-), and HER positive (HR-, HER2+). Results: We identified 805 bone only metastasis patients with positive bone biopsies, 395 (49%) of which had hormone receptor and HER2 characterization available. Of these 395 patients, 293 (74%) were luminal A-like, 44 (11%) were luminal B-like, 51 (13%) were triple negative, and 7 (2%) were HER2 positive. Of these patients, we identified 281 patients with tumor subtype data available for both primary breast biopsy and bone metastasis biopsy, of which 237 (84%) were concordant, while 44 (16%) were discordant (Table 1). Table 1. Concordance between breast and bone biopsies based on initial breast biopsy tumor subtypeBreast Biopsy Tumor Subtype (n = 281)Concordance with Bone Biopsy Tumor SubtypeDiscordant Bone Biopsy Tumor SubtypeLuminal A-like, HR+ HER2- (225/80%)Concordant: 199 (88%), Discordant: 26 (12%)10 Luminal B-like, 16 Triple negativeLuminal B-like, HR+ HER2+ (33/12%)Concordant: 19 (58%), Discordant: 14 (42%)11 Luminal A-like, 2 Triple negative, 1 HER2 positiveTriple negative, HR- HER2- (20/7%)Concordant: 16 (80%), Discordant: 4 (20%)3 Luminal A-like, 1 Luminal B-likeHER2 positive, HR- HER2+ (3/1%)Concordant: 3 (100%), Discordant: 0 (0%)NA Conclusions: When available, bone biopsy tumor subtype had significant concordance with breast biopsy tumor subtype in this large study of bone only metastasis patients. Discordant tumor subtype results were more common in patients with luminal B-like tumor subtype on initial breast biopsy. Citation Format: Parkes AM, Clifton KK, Al Awadhi A, Oke OC, Warneke CL, Litton JK, Hortobagyi GN. Tumor subtype concordance between breast and bone biopsies in bone only metastasis patients [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-16-01.