Letter: BST and cancer

From SAMUEL EPSTEIN

Ben Mepham and Paul Schofield are to be commended for their comments on the
hazards of BST milk (Letters, 10 September). However, their flat dismissal of
concerns relating to potential risks of breast cancer, particularly from
consumption of BST milk by infants, reflects surprising unfamiliarity with a
wide range of published scientific evidence.

There are close biological similarities, including an identical amino acid
sequence, between bovine and human IGF-1. IGF-1 is neither inactivated by
digestion nor destroyed by pasteurisation, which actually increases IGF-1
levels by some 70 per cent. Intact proteins, let alone smaller polypeptide
molecules such as IGF-1, are absorbed across the human gut wall, particularly
in infants.

A 1990 Federal Drugs Administration publication, based on unpublished
Monsanto data, revealed that short-term oral administration of IGF-1 to adult
rats induced statistically significant gross growth promotion even at the
lowest level tested, approximately 1/4000th of the positive infusion control
level.

Administration of BST to cows induced a very pronounced uptake of IGF-1 in
mammary epithelial cells. IGF-1 is a potent mitogen [causing cell division]
for cultured human breast epithelial cells. Truncated IGF-1, present at
estimated levels of 3 per cent in BST milk, is an even more potent mammary
mitogen. IGF-1 and related growth factors have been incriminated in promoting
the malignant transformation of normal human breast epithelia. IGF-1 has been
incriminated in maintaining the malignant phenotype of human breast
cancer.

The undifferentiated prenatal and infant human breast is particularly
susceptible to hormonal influences, so that imprinting by IGF-1 may not only
itself constitute a potential breast cancer risk factor, but may also increase
the sensitivity of the breast to subsequent unrelated carcinogenic risk
factors.

Such converging lines of evidence clearly raise unresolved questions on the
role of IGF-1 in BST milk as a potential breast cancer risk factor. Failure to
investigate such concerns, let alone dismissing them, is public health
folly.

Samuel Epstein

University of Illinois Medical

Center Chicago

UNIVERSITY OF ILLINOIS MEDICAL CENTER, CHICAGO