Clinical outcome of adjuvant radiotherapy for squamous cell carcinoma of the breast; a multicenter retrospective cohort study

BACKGROUND: Because primary squamous cell carcinoma (SCC) of the breast is a rare disease, the standard therapy has not been established. We examined the clinical outcomes of postoperative adjuvant radiotherapy for breast SCC. MATERIAL AND METHODS: We conducted a multicenter retrospective cohort study. Patients diagnosed with primary breast SCC who received adjuvant radiotherapy as part of their primary definitive treatment were included. Overall survival (OS), breast cancer-specific survival (BCSS), and recurrence-free interval (RFi) were evaluated. RESULTS: Between January 2002 and December 2017, 25 breast SCC patients received adjuvant radiotherapy as a primary treatment were included. Median follow-up time was 43.5 months. Three (12%), fifteen (60%) and seven (28%) patients had clinical stage I, II and III disease, respectively. Fourteen patients underwent breast-conserving surgery and subsequent adjuvant radiotherapy. Eleven patients underwent mastectomy and post-mastectomy radiotherapy. Ten patients received regional lymph node irradiation. Nine (36%) patients had disease recurrence. The first site of recurrence was locoregional in five, but distant metastasis arose in one. Concurrent local and distant metastasis were seen in two. Six cases of local recurrence occurred within the irradiated site. Seven patients died, and six of the deaths were due to breast cancer. Five-year OS, BCSS, and Rfi were 69%, 70%, and 63%, respectively. In multivariate analysis, age and lymphatic invasion were associated with increased risk of recurrence. CONCLUSION: Breast SCC has a high incidence of locoregional recurrence and poor prognosis. Age and lymphatic invasion are significant risk factors for recurrence.