Background: Cancer patients are at high risk of developing a second cancer after the treatment of initial cancers. Understanding the characteristics of multiple primary cancer is important to establish an effective surveillance program for the early detection of second cancers.
Methods: We analyzed the cancer registry records from 1986 to 1995 at the Cancer Institute Hospital. The combination of the sites of the index and second cancers and the time intervals between the two cancers were examined. For colorectal cancer, another database of patients between 1946 and 1991 was analyzed, with special reference to synchronous and metachronous cancers.
Results: Out of 24,498 registered cases, there were 1281 (5.2%) multiple cancers, of which 464 (1.9%) were in the same organs and 817 (3.3%) were in other organs. Gastric or colorectal cancer frequently developed as the second cancer regardless of the site of the index cancer. Although the majority of the second cancers developed within 3 years after the index cancer, some developed 5 years or more after the index cancer. In colorectal cancer, the cases with metachronous cancer were similar to those with hereditary nonpolyposis colon cancer. The frequent combination of an advanced index cancer and an advanced second cancer and relatively poor survival after the second cancers in the metachronous cases may reflect delayed diagnosis of the second colorectal cancer.
Conclusion: Careful attention should always be paid to the second cancer in treating cancer patients. Further analysis by individual site of the index cancers is needed to construct an effective surveillance for second cancers.