careful about generalizing, strenuous exercise decreases bc risk

[Lani]

but separating breast cancer into only ER+ and ER- fails to take the special behavior and history of her2+s into account. As only ~10% of breast cancer is Her2+ER+ and about 12% her2+ ER-, it is unlikely that if these subsets showed a different effect from strenuous exercise that it would have substantially altered these results as this large group of patients. Will check article to see if they even mention her2:

Strenuous exercise protects against invasive ER-negative breast cancer
Five hours of strenuous exercise a week cuts women's risk of both in situ and invasive breast cancer, report US researchers.

Protection against invasive disease was limited to patients with estrogen receptor (ER)-negative tumors, suggesting exercise could be highlighted as a complementary preventive measure to anti-estrogen treatment.

Physical activity is known to lower breast cancer incidence but few studies have examined the association separately for in situ and invasive disease, or considered hormone receptor (HR) status, said lead author Leslie Bernstein from the University of Southern California in Los Angeles.

The team analyzed data on the exercising behavior of 110,599 women participating in the California Teacher's Study, which began in 1995-1996. The researchers studied how much each woman exercised per week from high school to age 54 years. Breast cancer incidence was assessed from California's statewide cancer registry.

During 7 years of follow-up, 2649 women were diagnosed with invasive breast cancer and 593 with in situ breast cancer.

Invasive breast cancer was reduced in women who did strenuous exercise such as swimming, jogging, or aerobics for at least 5 hours a week, compared with the least active women, the team reports in the Archives of Internal Medicine. In situ breast cancer followed a similar pattern.

But the researchers were surprised to find that the benefit of long-term strenuous activity on rates of invasive breast cancer was only seen in patients with ER-negative tumors.

"This finding was somewhat unexpected; however, if it is repeated in future studies of physical activity and breast cancer risk, it offers a promising complement to our current approaches to preventing breast cancer, namely the use of drugs that block estrogens," they say.

Liz Carroll, Head of Clinical Services at the UK charity Breast Cancer Care said: "More and more evidence is emerging clearly pointing to the potential benefits exercise may have in reducing the risk of breast cancer. However, much more research is needed on the type and amount of exercise needed."



Arch Intern Med 2007; 167: 408–415