Multiple Primary Malignant Tumors - A Clinical Analysis of 15,321 Patients with Malignancies at a Single Center in China.

Background: Multiple primary malignant tumors (MPMTs) are defined as two or more histologically distinct malignancies in one individual, standard treatments for MPMTs are not well established, we aimed to clinical analyze the factors influence the treatment efficacy of MPMTs. Methods: This study retrospectively analyzed 15,321 malignant tumor patients at the Sir Run Run Shaw Hospital, College of Medicine, Zhejiang University, China, between March 2006 and June 2016. The survival analysis was performed with SPSS version 22.0 (SPSS Inc., Chicago, IL, USA) with Kaplan-Meier methodology. Results: The prevalence of MPMTs in our study was 1.09% (167/15321), with a male to female ratio of 2.34:1. Specifically, 98 patients harbored synchronous MPMTs, and 69 patients harbored metachronous MPMTs. The most common cancer pairs were digestive-digestive tumor (43 patients, 25.75%), digestive-lung cancer (32 patients, 19.16%), and head & neck-digestive tumor (11 patients, 6.59%). Among patients with synchronous and metachronous first primary cancers, 65.86% received surgery. 33.33% (27/81) of the patients with synchronous MPMTs received simultaneous resection. Of the 69 patients with metachronous MPMTs, 31.88% (22/69) were treated with surgery alone, 62.32% (43/69) received chemotherapy and/or radiotherapy for the first primary tumor, and 44.93% (31/69) received surgery for the other primary tumor. 98.20% (164/167) of patients with MPMTs were effectively followed up, the overall 2- and 5-year survival rates were 54.3% and 31.4%, respectively, with a median survival time of 28.0 months. Conclusions: The early diagnosis of rare MPMTs should not be neglected in patients not only when treated for a primary malignancy but also during long-term follow-up. Effective treatment for MPMTs may yield promising curative effect and warrants further investigation.