Characteristics and survival analysis of breast cancer survivors with metachronous double primary cancers: a retrospective cohort study.

Background: Breast cancer (BC) is the most frequently diagnosed malignancies in females, and its incidence has increased dramatically recently. Clinical studies have shown that BC patients are developing double primary cancers more frequently than by chance, and the prognosis has changed greatly. Previous articles rarely mentioned metachronous double primary cancers in BC survivors. Thus, further analysis of the clinical characteristics and survival differences may provide valuable information in BC survivors. Methods: In this study, we retrospectively analyzed 639 cases of double primary cancers in BC patients. Cox univariate and multivariate regression analyses of clinical factors of overall survival (OS) were performed in patients with double primary cancers when breast cancer was the primary tumor to assess the correlation between clinical factors and OS in these patients with double primary cancers. Results: Among the double primary cancer patients, BC was the most frequent first primary cancer. In terms of numbers, thyroid cancer was the most common type of double primary cancer among BC survivors. Patients had a younger median age when BC occurred as the first primary cancer rather than the second primary cancer. The total mean time interval between the onset of double primary tumors was 70.8 months. With the exception of the thyroid and cervical cancer, the incidence of second primary tumors was <60% within 5 years. However, the incidence was >60% within 10 years. The mean OS of double primary cancer patients was 109.8 months. Additionally, patients who had thyroid cancer as their second primary cancer had the highest 5-year survival rate, followed by cervical, colon, and endometrial cancer, while patients who had lung cancer as their second primary cancer had the lowest 5-year survival rate. OS risk of BC survivors with second primary cancers was significantly associated with age, menopause status, family history, tumor size, lymph node metastasis, and human epidermal growth factor receptor 2 (HER2) status. Conclusions: The identification of double primary cancers in earlier stages could play a critical role in guidance and lead to better outcomes. A prolonged follow-up examination period for BC survivors is needed to provide better guidance and treatments.