Breastfeeding and reduced risk of breast cancer in an Icelandic cohort study.

Case-control studies on the association between breastfeeding and the subsequent risk of breast cancer have given inconsistent results. To date, only two cohort studies have been reported on this subject. The present nested case-control study uses data from an Icelandic cohort of 80,219 women visiting a Cancer Detection Clinic that offers population-based cervical and breast cancer screening, in the years 1979-1995. The 993 parous cases were aged 26-90 years at diagnosis, with 9,729 parous controls individually matched on birth year, vital status at case diagnosis, and age when giving information on several potential risk factors for breast cancer. Using conditional logistic regression and confining the analysis to the 84 cases who were <40 years at diagnosis, an inverse association was evident between total duration of breastfeeding and breast cancer, with the adjusted odds ratio = 0.77 per 6 months' increase in duration of breastfeeding (95% confidence interval: 0.59, 1.00), whereas for the remainder of the women, a much weaker trend was observed. Ever lactating was associated with decreased risk, with the adjusted odds ratio = 0.33 (95% confidence interval: 0.19, 0.56) for women diagnosed at all ages. This is the first cohort study to indicate a negative association between breastfeeding and breast cancer.

Survival and prognostic factors of endometrial cancer patients in Iceland 1964-1985: can attendance at population-based Pap-smear screening affect survival?

After histological review of all cases registered during the period 1964-1985 at the Cancer Registry, 260 cases with endometrial carcinoma were eligible for analyses of survival rates and prognostic factors, as well as the association of Pap-smear screening attendance with these factors and survival. The total age-adjusted 5- and 10-year relative survival rates were 76% and 75%, respectively. The prognostic factors were tested by univariate analysis and simultaneously by a multivariate analysis using the Cox proportional hazards model. Factors that independently gave a less favorable prognosis were non-attendance at screening, older age at diagnosis, deep myometrial invasion, advancing stages and tumor grading, radiotherapy only, extra-genital symptoms and histology types of serous, clear cell and undifferentiated tumors (histologic type 3). Tested simultaneously with the Cox proportional hazards model, parameters that maintained a less favourable prognosis were grade 3, stage III-IV, deep myometrial invasion, older age, radiotherapy only and extra-genital symptoms. In addition, screening attendance showed significant interaction with age. In stages III and IV only grade 3 maintained a significantly less favorable prognosis. We conclude that our results indicate that attendance at Pap-smear screening (taking Pap smears and screening for genital symptoms) has a favorable prognostic value, especially among women under the age of 62.