Trends in cancer risks among Swedish agricultural workers

The Swedish Cancer-Environment Register was used to study time-related trends in relative risks (RRs) of cancer between 1961 and 1979 in a cohort of 254,417 Swedish men who were employed in agriculture in 1960. The reference cohort consisted of 1,725,845 Swedish men who were gainfully employed in economic activities other than agriculture or forestry in 1960. Altogether 24,763 cancers were observed in the study cohort and 146,900 in the reference cohort, giving an estimated RR for the entire study period of 0.82 (95% confidence interval: 0.81-0.83). The RR for all sites combined increased from 0.80 in 1961-73 to 0.84 in 1974-79 (P less than .01). The RR also increased over time for primary liver cancer (P less than .01), prostate cancer (P less than .01), cancer of other genital organs (P less than .01), cancer of urinary organs (P less than .01), lip cancer (P less than .05), and cancer of the nose and nasal cavities (P less than .05). For most of these sites the RR remained lower than unity. For prostate cancer, however, the RR was unity at the end of the study period. A decrease in the RR over time was observed for skin carcinomas of the trunk and limbs (P less than .05) and malignant tumors of the nervous system (P less than .05). For 27 of the 48 analyzed tumor sites the RR for the entire period 1961-79 was significantly lower than unity. The lowest RRs were seen for cancer of the pleura (0.25), cancer of the larynx (0.35), lung cancer (0.36), cancer of the hypopharynx (0.36), cancer of the floor of mouth (0.40), primary liver cancer (0.44), and cancer of the kidney pelvis (0.49). RRs significantly higher than unity were found for cancer of the lip (1.92), malignant melanoma, and carcinoma of the skin in the head and neck region (1.39 and 1.15, respectively), multiple myeloma (1.20), and cancer of the stomach (1.07).