Page 342 - 20dynamics of cancer

APPENDIX: INCIDENCE 327

Sex Differences in Incidence

Figures A.13–A.18 show the male:female ratios for the major adult
cancers. The plots highlight two kinds of information. First, the val-
ues on the y axis measure the male:female ratio, with positive values
for male excess and negative values for female excess. The scaling is
explained in the legend of Figure A.13. Second, the trend in each plot
shows the relative acceleration of male and female incidence with age.
For example, in Figure A.13, the positive trend for lung cancer shows
that male incidence accelerates with age more rapidly than does female
incidence, probably because males have smoked more than females, at
least in the past. Positive trends also occur consistently for the colon,
bladder, melanoma, leukemia, and thyroid. Negative trends may occur
for the pancreas, esophagus, and liver, but the results for those tissues
are mixed among locations. Simple nonlinear curves seem to explain
the patterns for the stomach and Hodgkin’s, and maybe also for oral-
pharyngeal cancers.
The patterns of relative male:female incidence probably arise from
differences between males and females in exposure to carcinogens, to
expression of different hormone profiles, or from different patterns of
tissue growth, damage, or repair. At present, the observed patterns
serve mainly to guide the development of hypotheses along these lines.