The incidence of atypical femoral fractures in breast cancer patients with bone metastases who received bisphosphonate treatment

Background Atypical femoral fractures (AFFs) have been reported to occur in patients with bone metastases who received long-term bisphosphonate treatment. However, the incidence of AFFs in breast cancer patients with bone metastases who received intravenous bisphosphonate is unclear. The purpose of this study is to examine the incidence of AFFs in breast cancer patients with bone metastases who received intravenous bisphosphonate. In addition, we estimated the number of dose and duration of intravenous bisphosphonate at the time of occurrence of AFFs. Methods We identified 356 female breast cancer patients with bone metastases who received intravenous bisphosphonate between November 2004 and October 2013 in our institution. The median number of doses of intravenous bisphosphonate was 18 (range, 1–103). The median duration of intravenous bisphosphonate treatment was 16 months (range, 1–102 months). We estimated the incidence of AFFs in patients who received intravenous bisphosphonate and used Poisson regression model to obtain the incidence rates of AFFs. Results Three AFFs in two patients were identified and the estimated incidence of AFFs was 2.99 per 1000 person-years. At the time of occurrence of AFFs, the patients had received 41 and 83 doses of intravenous bisphosphonate, for 37 and 79 months, respectively. The patients underwent open reduction and internal fixation with intramedullary nail. The frequency and incidence of AFFs in patients who received intravenous bisphosphonate for at least 41 or 83 doses or for more than 37 or 79 months were 2/60 (3.3%), 1/7 (14.3%), 2/70 (2.9%), and 1/9 (11.1%), respectively. Conclusions The incidence of AFFs is low in breast cancer patients with bone metastases who received intravenous bisphosphonate. Careful observation is warranted and radiography should be performed to investigate AFFs when clinical signs such as thigh pain appear. Study design Clinical study.