Do prognoses of patients with second primary cancers differ from those of patients with no prior cancer? A population-based study

Some cancer survivors develop second primary cancers. However, differences in prognosis between patients who have and have not had prior cancer have not been established. We examined and compared the prognoses of such patients. Using the record-linked database of the population-based Cancer Registry of Osaka Prefecture and Vital Statistics in Japan, we identified patients aged ≥ 40 years who were diagnosed with stomach (n = 70,946), colorectal (n = 60,582), or lung (n = 58,016) cancers during 1995–2009. We defined these cancers as index cancers. Patients were classified into three groups according to history of prior cancer and interval between diagnosis of index and prior cancer: single (no prior cancer or interval of ≥10 years), synchronous (interval ≤3 months), and metachronous (interval 3 months to 10 years). The 5-year prognosis from index cancer diagnosis was investigated using the Kaplan–Meier method and log-rank test. 5-year prognoses of patients with synchronous stomach and colorectal cancers were significantly worse than that of patients with single primary, about 60 % of these patients' deaths being attributable to the prior cancer. In contrast, 5-year prognoses of patients with metachronous primaries were not significantly worse, except for men with colorectal cancer. The percentages of index cancer deaths were 1.7–4.3 times those for non-index cancer deaths. A prior cancer contributed to an inferior prognosis in patients with synchronous stomach and colorectal cancers. The prognoses of patients with metachronous primaries were more affected by the index than by the prior cancer, whereas most of them had similar or better prognoses than did patients with a single primary. This finding would help to relieve cancer survivors' anxiety about their development and prognosis of metachronous second primary cancer.