Increased risk of secondary cancers in patients with primary cutaneous T cell lymphoma.

As putative etiologic factors of primary cutaneous T cell lymphomas may have a general cancerogenic effect, we wanted to assess the risk of secondary malignancies in 319 patients diagnosed with histopathologically verified cutaneous T cell lymphomas and reported to the Finnish Cancer Registry during the years 1953-95. Standardized incidence ratios were defined as the ratio of observed to expected numbers of cases. To obtain the expected numbers of cancer, age-, sex-, and period-specific Finnish incidence rates were applied to the appropriate person-years under observation. Ninety-five percent confidence intervals were calculated assuming a Poisson distribution. For the whole period, we detected 36 secondary cancers whereas 26 were expected (standardized incidence ratios 1.4, 95% confidence intervals 1.0-1.9). The overall risk of lung cancer was significantly increased (standardized incidence ratio was 2.7, 95% confidence intervals were 1.4-4.8); and in particular small-cell lung cancer showed high standardized incidence ratios (standardized incidence ratio was 8.5, 95% confidence intervals were 2.8-20). Also, the risk of lymphomas was elevated (standardized incidence ratios for Hodgkin and non-Hodgkin lymphomas combined were 7.0, 95% confidence intervals were 1.9-18). The incidence of other cancers was similar to the national ratios. An increased risk of secondary cancers and in particular small-cell cancer of the lung and lymphomas among patients with primary cutaneous T cell lymphoma is demonstrated. In clinical practice, lung cancer and lymphomas must be kept in mind when following up patients with cutaneous T cell lymphomas.