The effects of twins, parity and age at first birth on cancer risk in Swedish women.

The effect of reproductive history on the risk of cervical, colorectal and thyroid cancers and melanoma has been explored but the results to date are inconsistent. We aimed to examine in a record-linkage cohort study the risk of developing these cancers, as well as breast, ovarian and endometrial cancers, among mothers who had given birth to twins compared with those who had only singleton pregnancies. Women who delivered a baby in Sweden between 1961 and 1996 and who were 15 years or younger in 1961 were selected from the Swedish civil birth register and linked with the Swedish cancer registry. We used Poisson regression to assess associations between reproductive factors and cancer. Twinning was associated with reduced risks of breast, colorectal, ovarian and uterine cancers, although no relative risks were statistically significant. The delivery of twins did not increase the risk of any cancers studied. Increasing numbers of maternities were associated with significantly reduced risks of all tumors except thyroid cancer. We found positive associations between a later age at first birth and breast cancer and melanoma, while there were inverse associations with cervix, ovarian, uterine and colorectal cancers. These findings lend weight to the hypothesis that hormonal factors influence the etiology of colorectal cancer in women, but argue against any strong effect of hormones on the development of melanoma or tumors of the thyroid.

A randomized controlled trial to assess sunscreen application and beta carotene supplementation in the prevention of solar keratoses.

BACKGROUND: Solar keratoses (SKs) are among the strongest determinants of skin cancer, but little is known about the success of measures to control these common skin tumors. OBJECTIVE: To determine whether daily sunscreen application and/or beta carotene supplementation retards the rate of occurrence of SKs in adults in the medium term. DESIGN: Randomized controlled trial conducted between February 1992 and August 1996. SETTING: General community of the subtropical township of Nambour, Australia (latitude, 26 degrees south). PARTICIPANTS: A total of 1621 adults aged 25 to 74 years. Interventions Participants were randomized to daily use of sunscreen (application of a high-protection sunscreen to their head, neck, arms, and hands every morning) or application of sunscreen at their usual discretionary rate. They were also randomly assigned to take either one 30-mg tablet of beta carotene or one placebo tablet each day. MAIN OUTCOME MEASURE: Change in the prevalent number of SKs in the intervention group relative to change in the control group. RESULTS: The ratio of SK counts in 1994 relative to 1992 was lower in people randomized to daily sunscreen use (1.20; 95% confidence interval, 1.04-1.39) than in those randomized to discretionary sunscreen use (1.57; 95% confidence interval, 1.35-1.84). This 24% reduction is equivalent to the prevention of an average of 1 additional SK per person over that time. A reduction in the rate of change of SK prevalence was also seen in the sunscreen intervention group relative to the discretionary sunscreen group between 1994 and 1996, but it was not significant. No effect on the rate of change of prevalent SK counts was seen among those taking beta carotene supplements relative to those taking placebo tablets. CONCLUSIONS: Daily application of sunscreen retarded the rate of SK acquisition among adults in a subtropical environment, while a beta carotene supplementation of 30 mg/d had no influence on the occurrence of SKs.

Susceptibility to basal cell carcinoma is associated with high dermal mast cell prevalence in non-sun-exposed skin for an Australian populations.

In a Danish population, basal cell carcinoma (BCC) patients have a higher dermal mast cell prevalence in buttock skin than controls. This finding was supported by a functional link in mice between histamine-staining dermal mast cells and the extent of susceptibility to UV-B-induced systemic immunomodulation. It was important to confirm that this association was maintained in an Australian population with very different ancestry and sun exposure patterns. Australian BCC patients (n = 26) had significantly higher densities of mast cells in the dermis of buttock skin than control subjects (n = 25) (P = 0.0003, Mann-Whitney U-test). However, this correlation was lost at the sun-exposed site of the hand (P = 0.547, Mann-Whitney U-test). To further evaluate whether a relationship exists between dermal mast cell prevalence in sun-exposed skin and incidence of BCC in a larger study, biopsies of dorsal hand skin were obtained from an age-stratified random sample of 166 Queensland subjects, together with the 51 South Australian subjects, and dermal mast cell prevalence was quantified. Older subjects (over the median age of 42 years) had a greater incidence of BCC development (P = 0.0001, chi-square test) and significantly higher mast cell densities in hand skin (P = 0.0001, chi-square test) than younger subjects. However, mast cell density in sun-exposed hand skin was not significantly associated with BCC incidence. Finally, cellular expression of c-kit correlated with mast cell prevalence in non-sun-exposed skin, thereby implicating the stem cell factor-c-kit axis in the intrinsic mechanisms that regulate prevalence. These results show that high prevalence of dermal mast cells in buttock skin but not hand is associated with BCC development in an Australian population.

Longitudinal study of melanocytic nevi in adolescents.

BACKGROUND: Although melanocytic nevi are the strongest known risk factors for melanoma, their etiology is not well understood. OBJECTIVES: This study was performed to assess the roles of constitutional pigmentary factors and sun exposure in the development of new nevi in adolescents. METHODS: A cohort of 111 school children, aged 12 and 13 years at baseline, were followed up for 5 years. Whole-body counts of nevi of all sizes and detailed sun exposure histories were updated each year. Analyses of full-body nevus counts and of nevus counts on the face and neck region and on the shoulder and back region were undertaken by means of log-linear regression, allowing for repeated measures. RESULTS: Mean whole-body nevus counts were 130.1 (SD = 69.9) in 1990 and 215.5 (SD = 127.1) in 1994. Shoulder and back counts were consistently higher than face and neck counts. Subjects with heavy shoulder freckling had increased nevus counts on all sites investigated, with a means ratio for whole-body counts of 1.11 (95% CI, 1.03-1.19), compared with those with no freckling. Those who spent all of their school lunch times in the midday sun had a means ratio of 1.62 (95% CI, 1.15-2.29) compared with those who spent very little time in the sun during the lunch period. Summer holiday sun exposure was not significantly associated with development of nevi in this adolescent cohort. CONCLUSION: The degree of freckling, especially on the shoulders, and habitual midday sun exposure, rather than holiday sun exposure, are significant determinants of melanocytic nevi in Queensland adolescents.

Evolution of melanocytic nevi on the faces and necks of adolescents: a 4 y longitudinal study.

All melanocytic nevi on the faces and necks of a cohort of students, initially aged 12-14 y, were mapped and photographed annually for 4 y. The features of each nevus were charted yearly noting changes in size and profile, and the appearance or disappearance of any nevi on a student's face and neck was recorded. Nevi were classified by size (small, < 2 mm; medium, 2-5 mm; large, > 5 mm), and by profile (flat, raised). Data from 20 adolescents selected randomly from the cohort for detailed analysis showed males had about twice as many nevi as females, but there was little difference between sexes in their patterns of nevus development. Approximately half the nevi were small in all years; under 5% were large. Over the 4 y of follow-up the proportion of flat nevi dropped from 70% to 57%, whereas nevus numbers increased by 47% in year 1, with smaller increases in older students. Most new or disappearing nevi were small and flat, although both incident and disappearing nevi could be larger and/or raised. Of the existing nevi that altered in the follow-up period, the tendency was towards an increase in size among raised but not among flat nevi; a lowering of profile among small nevi; and a raising of profile among larger nevi; but there were many exceptions to this pattern. Among several host factors examined, inability to tan after sun exposure was found to be significantly negatively associated with the propensity of nevi to change size over the study period. Overall our findings indicate that, contrary to conventional belief, there is a measurable turnover among melanocytic nevi even in early life.