Abstract
PURPOSE: The pattern of double primary cancer after treatment for breast cancer is important for patient survival. MATERIALS AND METHODS: We analyzed 108 cases of metachronous double primary cancer in breast cancer patients treated from 1999 to 2012. RESULTS: Metachronous double primary cancers occurred in 108 of 2,657 patients (4.1%) with breast cancer. The median time to the occurrence of second cancer after diagnosis of the first was 58.4±41.2 months (range, 6.9 to 180.2 months). The most common cancer was thyroid cancer, which occurred in 45 patients (41.7%). This was followed by gastric cancer in 16 patients (14.8%), endometrial cancer in 10 patients (9.3%), and cervical cancer in seven patients (6.5%). The relative risk showed a significant increase in endometrial (4.78; 95% confidence interval [CI], 1.66 to 13.79), gastric (2.61; 95% CI, 1.68 to 4.06), and thyroid cancer (1.95; 95% CI, 1.37 to 2.79). At 5 years after diagnosis of breast cancer, secondary cancer occurred in 48 patients (44.4%), with 50.0% of the endometrial, 56.3% of the stomach, and 37.8% of the thyroid cancer cases being diagnosed after 5 years. Median survival after diagnosis of the second cancer was 123.9±11.2 months. The prognosis was mainly influenced by the anatomic site. CONCLUSION: The incidence of endometrial, stomach, and thyroid cancer increased significantly after treatment with primary breast cancer, and survival was dependent on early detection and the type of second primary cancer. A prolonged follow-up examination for metachronous double primary cancer is needed to provide early detection and improve survival time in patients with breast cancer.