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.

Introduction:Intracystic (encysted) papillary cancer (IPC) is a rare entity of breast cancer accounting for approximately (1–2%) of all breast tumours [1], usually presenting in postmenopausal women and having an elusive natural history. The prediction of the biological behaviour of this rare form of breast cancer and the clinical outcome showed its overall favourable prognosis; however, its consideration as a form of ductal carcinoma in situ with non-invasive nature is to be reconsidered as it has been shown to present histologically with invasion of basement membrane and even metastasis [2]. The objective of this review is to shed some light on this rare, diagnostically challenging form of breast cancer, including its radiological, histological, and molecular characteristics and its pathological classification. The final goal is to optimize the clinical management including the role of sentinel lymph node biopsy (SLNB), general management with adjuvant radiotherapy (RT), mammary ductoscopy, and hormonal treatment.Methods:A literature review, facilitated by Medline, PubMed, and the Cochrane database, was carried out using the terms ‘Intracystic (encysted) papillary breast cancer’.Results:Intracystic papillary breast cancer (IPC) is best managed in the context of a multidisciplinary team. Surgical excision of the lump with margins in excess of 2 mm is considered satisfactory. Sentinel lymph node biopsy (SLNB) is recommended as data have shown the possibility of the presence of invasive cancer in the final histology. RT following IPC alone is of uncertain significance as this form of cancer is usually low grade and rarely recurs. However, if it is associated with DCIS or invasive cancer and found in young women, radiotherapy may be prudent to reduce local recurrence. Large tumours, centrally located or in cases where breast conserving surgery is unable to achieve a favourable aesthetic result, a skin sparing mastectomy with the opportunity for immediate reconstruction can be offered. Adjuvant endocrine therapy may be suggested as almost certainly these tumours are hormonal positive.Conclusion:Further research is required to determine the role of adjuvant radiotherapy and endocrine therapy in IPC. Understanding the low-grade nature of this form of breast cancer allows treatment options to be less radical and safely omitted.