Metachronous Double Primary Cancer after Treatment of Breast Cancer

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.