Our first paper reviewed methods for modelling variation in cancer incidence and mortality rates in terms of either period effects or cohort effects in the general multiplicative risk model. There we drew attention to the difficulty of attributing regular trends to either period or cohort influences. In this paper we turn to the more realistic problem in which neither period nor cohort effects alone lead to an adequate description of the data. We describe the age-period+ohort model and show how its ambiguities surrounding regular trends 'intensify'. We recommend methods for presenting the results of analyses based upon this model which minimize the serious risk of misleading implications and critically review previous suggestions. The discussion is illustrated by an analysis of breast cancer mortality in Japan with special reference to the phenomenon of 'Clemmesen's hook'.

A main concern of descriptive epidemiologists is the presentation and interpretation of temporal variations in cancer rates. In its simplest form, this problem is that of the analysis of a set of rates arranged in a two-way table by age group and calendar period. We review the modern approach to the analysis of such data which justifies traditional methods of age standardization in terms of the multiplicative risk model. We discuss the use of this model when the temporal variations are due to purely secular (period) influences and when they are attributable to generational (cohort) influences. Finally we demonstrate the serious difficulties which attend the interpretation of regular trends. The methods described are illustrated by examples for incidence rates of bladder cancer in Birmingham, U.K., mortality from bladder cancer in Italy, and mortality from lung cancer in Belgium.

Use of sunscreens is widely advocated as a preventive measure against sun-induced skin cancers. However, to date, no epidemiologic study has reported a decreased melanoma risk associated with sunscreen use. We have conducted a case-control study aimed at evaluating the influence of sunscreen use on the occurrence of cutaneous malignant melanoma. In 1991 and 1992, 418 melanoma cases and 438 healthy controls were interviewed in Germany, France and Belgium. The questionnaire used differentiated between regular sunscreens, psoralen sunscreen (prepared with 5-methoxypsoralen, a tanning activator and photocarcinogen), and self-tanning cosmetics (which produce a tan without ultraviolet radiation). After adjusting for age, sex, hair colour and holiday weeks spent each year in sunny resorts, the melanoma risk was of 1.50 (95% Cl:1.09-2.06) for regular sunscreens, and of 2.28 (95% Cl: 1.28-4.04) for psoralen sunscreens. No melanoma risk was associated with use of self-tanning cosmetics. Among subjects with a poor ability to tan, psoralen sunscreen users displayed a melanoma risk of 4.45 (95% Cl: 1.25-15.8) when compared with regular sunscreen users. There was a significant negative interaction between regular sunscreen use and sunburns experienced in adulthood. Use of sunscreens, especially psoralen sunscreen, was associated with higher density of pigmented lesions of the skin. Although we cannot exclude the presence of an unknown confounding factor, our results support the hypothesis that sunscreens do not protect against melanoma, probably because of their ability to delay or avoid sunburn episodes, which may allow prolonged exposure to unfiltered ultraviolet radiation. Serious doubts are raised regarding the safety of sunscreens containing psoralens.

A pilot case-control study on bladder cancer, with population-based controls matched for each of 74 cases, has been conducted in two industrial areas of Southern Belgium in order to analyze the influence of tobacco use and occupation. Observed bladder cancer risk for smokers is more than 5 times higher than that for non-smokers, and the risk for people having an a priori hazardous occupation is about 3.5 times higher than that of other subjects. A dose-response relationship was found for tobacco exposure and duration of employment. It seems that the risk is increased in a log-linear way by these variables. Population attributable risks show that in 20 cases of bladder cancer, 17 could be explained by the two factors combined. This study also reveals an increased risk for metal workers, truck and engine drivers, coal-miners, and rubber and coal-tar workers. The risk for metal workers is specially high in the case of turners, metal fitters, blacksmiths, stokers and workers exposed to hot metal.

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