An increase in epidermoid anal cancer has been observed in the past 30
years (1959-89). This increase in anal cancer has been noted to be mo
re pronounced in women than men. The absence of a significant interact
ive effect of the HIV and human papillomaviruses and the incidence of
anal cancer has been noted in some studies. These observations provide
the rationale for consideration of other aetiologic agents that may c
ontribute to the increase of anal cancer in men and women. Within the
context of their ability to serve as cancer initiating and promoting f
actors, spermatozoa and seminal plasma are suggested as aetiologic age
nts and/or cofactors which are common to men and women practising anal
intercourse in whom an increase in anal cancer has been observed. It
is further suggested that sexual behaviour, that is, anal intercourse,
not sexual preference, is one of the primary factors in the developme
nt of anal cancer.