Certain cancers are selective for a given gender due to the presence of a gender-specific organ, e.g. cancer of the uterine cervix in females and cancer of the prostate in males. However, for other cancers with a common target, there exists a definite dichotomy in epidemiological features:
- the majority of tumours have a higher incidence and mortality in males than females
- only tumours of the breast, gallbladder, right side of the colon, genital tract and thyroid have a higher incidence in females
- cancer of the breast is many hundreds of times more common in females than males, presumably because of the average greater volume of tissue which has a sustained exposure to physiological hormonal cycles
- cancer of the lung in females is increasing, probably because of an increase in smoking in this group; however, it is still less than male rates and this may be partly due to a genetic predisposition: lung cancer rates in male non-smokers are approximately 50% greater than female non-smoker counterparts
- some cancers have an extremely variable sex ratio depending on the age group and country examined, e.g. cancer of the oropharynx