http://jco.ascopubs.org/cgi/content/abstract/3/7/941
I have only seen the abstract of this. Something I found whilst looking for something else. Thought provoking.
http://jco.ascopubs.org/cgi/content/abstract/3/7/941
Journal of Clinical Oncology, Vol 3, 941-948, Copyright © 1985 by American Society of Clinical Oncology
ARTICLES
Plasma melatonin and the hormone-dependency of human breast cancer
DN Danforth Jr, L Tamarkin, JJ Mulvihill, CS Bagley and ME Lippman
"Further, a strong inverse correlation was observed between the plasma melatonin concentration and the quantities of ER and PR in the primary tumor: the lower the plasma melatonin concentration the greater the amount of either receptor in the primary tumor."
"These findings suggest an important relationship between the plasma melatonin diurnal rhythm and the hormone dependency of human breast cancer, and may have implications for both the prognosis and treatment of this malignancy."