CASE REPORT Chromosome 17 polysomy in circulating tumor cells in patients with metastatic breast cancer: a case series Naoki Hayashi • Seigo Nakamura • Hiroshi Yagata • Yuji Shimoda • Hidekazu Ota • Gabriel N. Hortobagyi • Massimo Cristofanilli • Naoto T. Ueno Received: 21 September 2010 / Accepted: 6 December 2010 / Published online: 6 January 2011 Ó Japan Society of Clinical Oncology 2010 Abstract The human epidermal growth factor receptor 2 (HER2) gene is located on the long arm of chromosome 17 (Chr-17). While primary tumors with Chr-17 polysomy (polysomy 17) are histopathologically similar to HER2- negative tumors, the role of polysomy 17 in circulating tumor cells (CTCs) is still unknown. We report the detec- tion rate of polysomy 17 in CTCs in patients with metastatic breast cancer (MBC). We determined the CTC count per 7.5 ml blood and polysomy 17 in CTCs at 3- to 4-week intervals up to 12 weeks in 52 patients. Polysomy was defined as Chr-17 C2.2. CTCs were detected in 40 of 52 patients (76.9%) during the study period, in 32 of the 52 patients (61.5%) at baseline, and in 21 of 49 patients (42.9%) at 3–4 weeks. Polysomy 17 in CTCs was present in 10 of 52 patients (19.2%) during the study period, in 5 of 52 patients (9.6%) at baseline, and in 7 of 49 patients (14.3%) at 3–4 weeks. The individual patient counts of polysomy 17 in CTCs/total count of CTCs examined for polysomy 17 at 3–4 weeks were 1/1, 1/7, 1/7, 2/27, 2/30, 2/50, and 3/50. Six of the 7 patients with polysomy 17 in CTCs had HER2- negative primary tumors. None of the CTCs displaying polysomy 17 themselves had HER2 amplification by FISH. In summary, polysomy 17 in CTCs was observed in only a small population of patients with MBC. We should pro- spectively evaluate its prognostic value in both HER2- positive and -negative metastatic breast cancer. Keywords Circulating tumor cell Á Breast neoplasm Á Polysomy Á HER2 Á Metastasis Introduction Human epidermal growth factor receptor 2 (HER2) expres- sion is an important prognostic factor of breast cancer. HER2 amplification or overexpression is found in 15–20% of breast cancers [1–4]. HER2-targeting therapy (trastuzumab or lapatinib) improves the prognosis of patients with HER2- amplified or -overexpressed breast cancer [5–8]. The HER2 gene is located on the long arm of chromo- some 17 (Chr-17q12) [9]. The existence of chromosome 17 polysomy (polysomy 17) in primary tumors has been examined [10–15]. Some studies have reported that poly- somy 17 may result in false-negative HER2-amplification findings or difficulty of HER2 assessment by fluorescence N. Hayashi Á G. N. Hortobagyi Á N. T. Ueno (&) Department of Breast Medical Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 1354, Houston, TX 77030, USA e-mail: nueno@mdanderson.org N. Hayashi Á S. Nakamura Á H. Yagata Department of Breast Surgical Oncology, St. Luke’s International Hospital, 9-1 Akashi-cho, Chuo-ku, Tokyo 104-8560, Japan N. Hayashi Á H. Ota Second Department of Pathology, The Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan S. Nakamura Department of Breast Surgical Oncology, The Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan Y. Shimoda Research and Development Department, SRL Inc., 5-6-50 Shin-machi, Hino, Tokyo 191-0002, Japan M. Cristofanilli Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111-2497, USA 123 Int J Clin Oncol (2011) 16:596–600 DOI 10.1007/s10147-010-0173-3