The incidence of non-Hodgkin's lymphoma (NHL) has been increasing rapidly o
ver the last three decades. The reasons for this trend are not known althou
gh increasing exposure to sunlight has been postulated. We used data from t
he New South Wales Central Cancer Registry to analyse second primary neopla
sms following NHL diagnosed between 1972 and 1995, to identify possible com
mon causal agents. A total of 12 452 patients contributed 54 308 person-yea
rs of follow-up during which time there were 705 second primary neoplasms c
ompared to 592.99 expected (standardized incidence ratio (SIR = 1.19, 95% c
onfidence interval (CI) 1.10-1.28). There were excesses of melanomas of ski
n (SIR = 2.38, 95% CI 1.92-2.91), lip cancer (SIR = 2.74, 95% CI 1.59-4.38)
, tongue cancer (SIR = 2.53, 95% Cl 1.09-4.99) and bladder cancer (SIR = 1.
64, 95% CI 1.19-2.21). There was also over a threefold excess in soft tissu
e sarcomas (SIR = 3.61, 95% CI 1.80-6.45) and in thyroid cancer (SIR = 3.42
, 95% CI 1.56-6.49). The SIR for myeloid leukaemia was 0.78 (95% CI 0.28-1.
69), The increases in melanoma of the skin and cancer of the lip and tongue
among patients with NHL strongly suggest sunlight exposure as a shared cau
sal agent. The increase in soft tissue sarcomas might be due to shared effe
cts of exposure to chemicals such as phenoxy acid herbicides. The increases
in bladder and thyroid cancers are likely to be explained by effects of tr
eatment for NHL. We did not find a chemotherapy related increased risk of m
yeloid leukaemia among NHL patients. (C) 2000 Cancer Research Campaign.