True recurrences and new primary tumors have different clinical features in invasive breast cancer patients with ipsilateral breast tumor relapse after breast-conserving treatment.

Ipsilateral breast tumor relapse (IBTR) after breast-conserving treatment (BCT) may represent two distinct types of lesion, including a true recurrence (TR) or a new primary tumor (NPT). The aim of this study was to ascertain the difference between TRs and NPTs and to show the clinical significance of classifying IBTR into these two types of recurrence. Patients (n = 2,075) with unilateral invasive breast cancer who underwent BCT between 1987 and 2005 at Saitama Cancer Center were analyzed. IBTR was classified into TR and NPT, which was based on all clinical and pathological features of both a primary tumor and IBTR that can be evaluated. IBTR-free survival and the risk factors were analyzed in order to compare the findings for TR and NPT. In addition, the salvage surgical methods for IBTR and overall survival after IBTR were analyzed. Sixty patients with IBTR were classified into 52 with TR and eight with NPT. IBTR-free survival was significantly shorter in the patients with TR than those with NPT. Young age, tumor size, a positive surgical margin, and omission of radiation therapy (RT) were significant risk factors for TR. Omission of RT was the only significant risk factor for NPT. In 27 patients who underwent a repeat lumpectomy for TR, four had a second IBTR. The overall survival after IBTR was worse in patients with TR than NPT. TR and NPT show quite different clinical features. Classifying IBTR into TR or NPT can therefore help to select the most appropriate treatment for IBTR.