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.
- • We examined the prognoses from diagnoses of second primary cancers (SPCs).
- • Synchronous SPCs (stomach, colorectal) had worse prognoses than a single primary.
- • Most metachronous SPCs had not so worse prognoses than a single primary.
- • SPCs affected the prognoses of patients with metachronous SPCs.
- • We need to active management of SPCs in patients with metachronous SPCs.
Cancer has been the commonest cause of death in Japan since 1981 . The lifetime odds of dying from cancer were 26.7 % for male and 17.8 % for female individuals in 2019 . With improvements in treatment strategies, patients’ life expectancies are improving. However, the longer the life expectancy, the higher the possibility of developing other diseases. In particular, the probability of developing a second primary cancer (SPC) also increases . Cancer survivors are therefore anxious about such a development and the possibility that an SPC could be fatal.
The prognosis of patients with multiple primary cancers (MPCs) needs to be examined regarding both the first primary cancer and SPC. Previous studies have reported that the prognosis of patients with second primary lung cancers is not worse than that of those with first primary lung cancers . However, there are few reports on the prognosis of patients with SPC, the exception being for second primary lung cancers . There are also few studies on the prognosis from the time of any SPC diagnosis in Japan, where SPCs are being increasingly identified . In these few studies, the prognosis of patients with non-small cell lung cancer did not differ from those of individuals without prior cancer, provided the prior cancer had been diagnosed more than 5 years previously . Additionally, diffuse large B cell lymphoma patients with a prior cancer reportedly have shorter survivals than those without prior cancer . When following up cancer survivors, it is important that clinicians understand their patients’ anxieties about SPCs and provide accurate information on their prognoses.
Information on the cause of death is useful when investigating the prognosis of patients with MPCs in that it contributes to assessment of the impact of each cancer . Several studies have used population-based cancer registries to investigate both the prognosis and cause of death among patients with prior cancer . For example, in one study, about 79 % of patients with a second hepatocellular carcinoma died of SPC-related causes; thus, the prior cancer did not substantially impact their survival . Determining how much of an impact each cancer has on the prognosis of patients with MPCs may be helpful in planning their treatment.
In this study, we aimed to examine and compare the prognosis from SPC diagnosis in patients with MPCs and the prognosis in patients with a single primary. We used data on cause of death to explore the prognostic impact of each cancer in patients with MPCs.