Recent increases have been reported in industrial countries for severa
l sites of cancer. The causes of these increases remain unknown. Effor
ts should proceed to identify those occupational groups with increases
in the same sites, as these may indicate relevant exposures. Two anal
yses were undertaken: trends in cancer mortality in industrial countri
es were reviewed to identify recently increasing sites and summaries w
ere compiled of studies on farmers which have shown increased risks-fo
r these same sites of cancer. Using data provided by the World Health
Organization, age-specific rates were developed for a number of sites
of cancer from 1968 to 1986. Trends in the ratio of male to female can
cer mortality were also assessed for several of these countries. Based
on a literature review by the National Cancer Institute, patterns of
cancer in farmers reported in 20 studies from 8 countries are summariz
ed, weighting each study by its size to create combined relative risks
. In industrial countries, rates of cancer mortality increased for a n
umber of sites, including melanoma, prostate, non-Hodgkin's lymphoma,
multiple myeloma, breast, brain, and kidney cancer. The ratio of male
to female cancer mortality (for all sites of cancer excluding lung) ha
s generally increased in several countries during this same time perio
d. Many of the same sites that have increased in the general populatio
n have also been found to be increasing in farmers. Significant excess
es occurred for Hodgkin's disease, multiple myeloma, leukemia, skin me
lanomas, and cancers of the tip, stomach, and prostate. Nonsignificant
increases in risk were also noted for non-Hodgkin's lymphoma and canc
ers of connective tissue and brain in many surveys. These excesses occ
urred against a background of substantial deficits among farmers for t
otal mortality, heart disease. and many other specific diseases. Epide
miologic studies of farmers, and other occupational groups with excess
rates of these same sites of cancer, may help to identify specific ca
usal exposures that partly account for the rising trend of certain can
cers in developed countries. Despite a number of common causes, heart
disease and some sites of cancer show opposite trends in the general p
opulation, with the former decreasing and the latter increasing. Thus,
the causes of the increases in cancer are not likely to stem from tho
se that are shared with heart disease, but to represent some as-yet-un
recognized risk factors. Among those that should be carefully reviewed
are solvents, pesticides, engine exhausts, and animal viruses, materi
als to which both farmers and the general population are exposed in in
creasing amounts.