This study indicates that PCBs and DDE contamination levels in adult women are not associated with increased risk of breast cancer. If anything, there is a slight but statistically insignificant decrease in risk associated with increasing levels of PCB and DDE in women's blood.

The question is how to interpret this result.

At one level it is very positive and reassuring. Taken at face value, women with higher levels of these two organochlorine contaminants during adulthood are not at greater risk as a result of that exposure.

This does not mean, however, that PCBs and DDE (or its parent compound, DDT) are absolved of involvement in the causation of breast cancer. The study examines only the relationship between adult contamination levels and risk. It gives no insight into risk and fetal or developmental exposure. One of the central theses of endocrine disruption is that developing stages of a person (or animal's) life cycle are more vulnerable than are adult stages. The 1999 assessment by the US National Academy of Sciences of health risks related to endocrine disruption explicitly acknowledges that research on human health impacts has failed to address this issue, concluding that the relevant studies simply haven't been done.

Nor does the paper by Hunter et al. say very much about other organochlorines, or about "xeno-estrogens" (synthetic compounds that mimic estrogen).

DDE in fact is an "xeno-anti-androgen," not a xeno-estrogen. Under certain experimental circumstances it can have effects superficially similar to xeno-estrogens because exposure to it causes experimentally exposed male mammals to develop characteristics that are more feminine than expected. The mechanism of action, however, is through its interference with androgens like testosterone (hence anti-androgen) instead of its enhancement of estrogens.

And it turns out that the forms of PCBs that accumulate and persist in the human body are anti-estrogens, not estrogens. So forget trying to reach sweeping conclusions about "weak xenoestrogens" from studies of DDE and PCBs measured in adult women. More...

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