Chains of evidence, mosaics of data: does estrogen ‘cause’ breast cancer? How would we know?

Abstract

There appears to be a broad consensus that estrogen is a cause of breast cancer. Proof of cause and effect in clinical medicine requires a different approach for an epidemiological exposure (a ‘mosaic’ approach) than for an infectious agent suspected of causing a particular disease (a ‘chain of evidence’ approach). This paper discusses the differences between these two approaches in determining the relationship between a risk factor and a disease, and assesses the strength of the data linking estrogen with breast cancer. Analysis of existing data, including findings from the Women's Health Initiative, finds that all nine of the criteria necessary for confirming the epidemiological strength of a risk factor are not met in the case of estrogen, raising serious questions about the validity of this widespread assumption.

Key words::

• BREAST CANCER
• CAUSATION
• ESTROGEN
• HORMONE REPLACEMENT THERAPY

Conflict of interest Dr Bluming was compensated on an hourly basis for serving as an expert witness on behalf of defendant Wyeth and Pfizer pharmaceuticals. He is a Master of the American College of Physicians, a Clinical Professor of Medicine at the University of Southern California, a former senior investigator for the National Cancer Institute and an oncologist/hematologist in private practice. Carol Tavris, PhD, is a social psychologist and writer, co-author of two leading psychology textbooks, and (with Elliot Aronson) of Mistakes were made (but not by me). Neither of them has a vested interest in defending the pharmaceutical industry nor have they accepted compensation for writing this article. Dr Tavris has long been a vociferous critic of pharmaceutical influence on medical research.

Source of funding Nil.