Racial, ethnic, and gender variations in cancer risk: considerations for future epidemiologic research.

There is no question that the risk of many cancers varies substantially by race, ethnic group, and gender. Although important clues to cancer etiology may come from investigating the differences in risk across subgroups of the population, epidemiologic research has often focused on white men. More descriptive and analytic studies are needed to identify and explain variations in risk among population subgroups. Especially important are studies to clarify the role of differential exposures, susceptibility, and diagnostic factors in cancer incidence, although differences in treatment may contribute to variations in cancer mortality. Improvements in classification of ethnicity, assessment of carcinogenic exposures in various subpopulations, and measures of host susceptibility states should augment future epidemiologic research designed to better understand mechanisms underlying the racial, ethnic, and gender differences in cancer risk

Menopausal oestrogens and breast cancer risk: an expanded case-control study.

A study among 1960 post-menopausal breast cancer cases and 2258 controls identified through a nation-wide screening program enabled evaluation of effects of oestrogen use on breast cancer risk. Ever use was not associated with increased risk (RR = 1.0), but a significant trend was observed with increasing years of use, with users of 20 or more years being at a 50% excess risk. Elevations associated with long-term use were apparent across all menopause subgroups (natural, ovaries retained, ovaries removed). Hormones exerted particularly adverse effects in those initiating use subsequent to a diagnosis of benign breast disease, particularly long-term users (RR = 3.0, 95% CI 1.6-5.5). There was also some indication that effects predominated among the lower stage tumours, an observation similar to that observed for endometrial cancer. These findings support a role for oestrogens in the aetiology of breast cancer, although risk appears to be enhanced only after extended periods of use, and not to the extent observed for other hormonally-sensitive tumours

Developing clues to environmental cancer: a stepwise approach with the use of cancer mortality data.

Clues to environmental determinants can often be derived from the patterns of mortality from cancer. This review focuses on the stepwise approach of using cancer mortality maps, supplemented by correlation studies linking mortality rates with demographic and industrial data at the county level, to generate hypotheses to cancer etiology which can then be pursued by analytical epidemiological studies. Advantages and limitations of this approach and its application in the study of lung cancer in the United States are described

Reproductive factors in the aetiology of breast cancer.

An interview study of 1,362 breast cancer cases and 1,250 controls identified through a multi-centre screening project allowed an evaluation of reproductive determinants of breast cancer. Risk increased linearly with age at first livebirth; women with a birth after age 30 showed 4-5-fold excess risks compared to those with a birth prior to 18, while the risk for nulliparous women resembled that for women whose first birth was in their late twenties. The protection conferred by an early first pregnancy prevailed for pregnancies that ended in a livebirth or stillbirth, but not for those that terminated in other outcomes. Among parous women, a first trimester abortion prior to a livebirth was not associated with an elevated risk, except in the event of multiple miscarriages (RR = 2.2, 95% Cl 0.9-5.1). Although numbers were limited, women who reported an induced abortion in the absence of ever having a livebirth showed some elevation in risk. Age at first livebirth explained most associations, but some residual reduction in risk was noted for multiparous women and those with several births at an early age. There was evidence that delays in birth after marriage increased risk, but this did not explain the high risk associated with late age at first birth

Smoking and biliary tract cancers in a cohort of US veterans.

Except for gallstones, the risk factors for cancers of the biliary tract (CBTs) are poorly understood. Recent case-control studies have suggested cigarette smoking as a potential risk factor. In a cohort study of nearly 250,000 US veterans whose mortality was followed for up to 26 years, we evaluated the risk of CBT associated with tobacco use. Relative risks (RRs) and corresponding 95% confidence intervals (CIs) were calculated. A total of 303 CBT deaths were observed during the follow-up period. Compared with those who had never used any tobacco, current cigarette smokers at entry to the cohort had a 50% excess risk of CBT (RR = 1.5, CI = 1.1-2.0). A nearly 2-fold risk was observed among those who smoked more than 20 cigarettes per day and among those who started smoking under age 20. Non-significant increases in risk occurred among smokers of other forms of tobacco. This cohort study is consistent with reports that smoking is a risk factor for CBT, but further studies are needed to clarify whether the effect is specific for certain subsites and whether it reflects an association with pre-existent gallstones

Cancer risk following pernicious anaemia.

A computer-based file of all Veterans Administration (VA) hospitalisation records for the period 1969-1985 was used to identify and follow for cancer development a cohort of 5,161 white males with pernicious anaemia. A total of 34,915 person-years were accrued, with an average length of follow-up of 6.8 years. A total of 481 cancers were diagnosed, slightly higher than the number expected (SIR = 1.2). Significant excesses were observed for cancers of the buccal cavity and pharynx (1.8) and stomach (3.2), and for melanoma (2.1), multiple myeloma (2.1), myeloid leukaemia (3.7) and other and unspecified leukaemia (4.0). Although the excess for stomach cancer was highest in the first year after diagnosis in a VA hospital, risks of 2-fold or greater persisted throughout the study period. The majority of leukaemias occurred in the first year of follow-up, but some excess risk continued beyond this time. The elevated risk of buccal and pharyngeal cancers may relate to heavy alcohol intake among this population, although risks remained high even when the cohort was restricted to patients without an admission for alcoholism. Although an elevated risk of stomach cancer among pernicious anaemia patients is consistent with most previous surveys, the low absolute risk suggests that the cost-effectiveness of intensive screening should be reassessed

Declining incidence is greater for esophageal than gastric cancer in Shanghai, People's Republic of China.

Temporal trends in the incidence of esophageal and gastric cancers during 1972 to 1989 were addressed in urban Shanghai, the location of China's longest standing cancer registry. Over the 18 year study period, esophageal cancer rates decreased more than 50% from 28.8/100,000 person-years in 1972-74 to 13.3/100,000 in 1987-89 among men and from 11.3/100,000 to 5.4/100,000 among women. Reductions were apparent in each age group, but most pronounced among younger generations, with more than a 75% decline in incidence among those under age 55 years. The incidence rate for stomach cancer among men decreased 20% from 62.0/100,000 in 1972-74 to 50.1/100,000 in 1987-89. The reduction among women, however, was minor, from 23.9/100,000 to 23.2/100,000. The patterns varied by age, with declines among persons 45-64 years and increases among those in older and younger age groups. The determinants of these trends are not clear, but appear related in part to dietary changes

Multiple primary cancers in Connecticut, 1935-82.

Recently, the National Cancer Institute published a comprehensive monograph on multiple primary cancers in Connecticut and Denmark. This paper summarizes some of the observations made on the Connecticut population. Data compiled by the Connecticut Tumor Registry have extended our knowledge about the patterns of multiple primary cancers, especially among long-term survivors of cancer and among patients with relatively rare tumors about which little information currently exists. When compared with the general Connecticut population, cancer patients had a 31 percent (RR = 1.31) increased risk of developing a second cancer and a 23 percent (RR = 1.23) elevated risk of second cancer at a different site from the first. Common environmental exposures seemed responsible for the excess occurrence of many second cancers, particularly those related to cigarette smoking, alcohol consumption, or both. For example, persons with epithelial cancers of the lung, larynx, esophagus, buccal cavity, and pharynx were particularly prone to develop new cancers in the same or contiguous tissue throughout their lifetimes. Cancers of the colon, uterine corpus, breast, and ovary frequently occurred together, suggesting underlying hormonal or dietary influences. Only patients with prostate cancer were at significantly low risk for second cancer development; this might be an artifact of case finding, since advanced age at initial diagnosis was generally associated with an underascertainment of second cancers. Radiotherapy may have caused rectal and other cancer among patients with cancers of the female genital tract, and leukemia among patients with uterine corpus cancer. Chemotherapy with alkylating agents probably contributed to the excess of acute nonlymphocytic leukemia following multiple myeloma or cancers of the breast and ovary. Genetic susceptibility seemed to explain some tumor complexes, such as the multiple occurrences of cutaneous melanoma and the excess of bone cancer following retinoblastoma. Research into multiple cancer syndromes should enhance our understanding of carcinogenic factors and mechanisms and the development of strategies for cancer prevention and control

Lung cancer and prior tuberculosis infection in Shanghai.

In a population-based case-control study of lung cancer in Shanghai involving interviews during 1984-86 with 1,405 cancer patients and 1,495 controls, a significant 50% elevation in the risk of lung cancer, adjusted for cigarette smoking, was observed among persons who had a history of tuberculosis. Among those diagnosed with tuberculosis within the past 20 years, the risk exceeded 2.5-fold. In males the lung cancers tended to occur on the same side as the previous tuberculosis infection. For both sexes, the effect of recent tuberculosis was most apparent for adenocarcinoma and peripheral tumours. No relationship was found between lung cancer risk and the type of tuberculosis therapy, including use of isoniazid. The findings suggest that tuberculosis may predispose to lung cancer, with the association most apparent among recent survivors of the infection