We studied the relation of certain endocrine-related variables among 23 cas
es of male breast cancer and 76 apparently healthy male controls. There wer
e significant inverse associations with smoking (P = 0.03), birth order (P
= 0.02) and reported frequency of orgasms in later life (P = 0.0004). The s
tudy provides strong indirect evidence that endocrine factors are important
in the aetiology of male breast cancer. (C) 2000 Cancer Research Campaign.