Teenage Hormones Cause More Than Angst
Hormones & Genetic History May Amplify Breast Cancer Risk

Is puberty a cancer risk? A study of female twins published in The New England Journal of Medicine found that puberty may increase the risk of breast cancer in women who carry a genetic predisposition to the disease.

A small portion of women who develop breast cancer have known genetic abnormalities, such as BRCA mutations, that raise their chances of getting the disease. Not much is known about what other factors work together with genetic mutations to cause cancer in breast cells.

Researchers Ann S. Hamilton and Thomas M. Mack reasoned that breast cancer must be influenced by other factors. In a Reuters Health interview, Hamilton explained, "We still have a lot to learn about breast cancer and the genetic factors that have been identified so far do not account for all the cases of breast cancer thought to be associated with genetic susceptibility."

One cause of breast cancer is thought to be excessive lifetime exposure to ovarian hormones such as estrogen. Perhaps the onset of puberty, menopause and age at first pregnancy might interact with the genetic history to affect the risk.

They examined 1,811 pairs of twins where either one or both of the twins had breast cancer. They looked for links between age at puberty, menopause and pregnancy and onset of breast cancer.

Twins where both developed the same type of breast cancer, disease-concordant twins, were assumed to have a hereditary predisposition, genetic mutations, that raised their risk.

They found that, in these pairs, the first twin to reach puberty was five times more likely to get breast cancer earlier.

Twins with nonhereditary breast cancer, where only one of the twins had been diagnosed with breast cancer, showed no relationship between the age of puberty and breast cancer risk.

In this group, the twin that had a later first pregnancy, fewer children, and later menopause showed an increased risk of breast cancer. In the twins where both developed breast cancer these factors did not seem to make a difference.

The researchers concluded that, "within the most genetically susceptible subgroup of twin pairs, the strong influence of earlier puberty on the age at the diagnosis of breast cancer and the absence of linkage to hormonal milestones later in life suggest that most cases of hereditary breast cancer are not related to cumulative hormone exposure and that they may instead result from an unusual sensitivity to pubertal hormones."

What does this mean to women who are at high risk of breast cancer?

It verifies that the genetic predisposition to breast cancer is affected by other factors. Earlier exposure to estrogen in the twin who reached puberty first meant earlier onset of breast cancer. Perhaps preventive treatments could be designed to interfere with the early effects of estrogen in women with hereditary breast cancer.

It adds concern about the increase in childhood obesity. Fat tissue may increase the effects of estrogen. If the hormones introduced at puberty affect the risk of developing breast cancer, then heavier girls are increasing this risk.

It adds one more piece to the puzzle of what causes breast cancer. Eventually there will be enough pieces to see the whole picture and design interventions to stop breast cancer before it starts.

Source: New England Journal Of Medicine June 5, 2003 Vol 348,23 pp. 2313-2322

Elsewhere on the Web:

Breast Cancer Link To Puberty?

Study Suggests Puberty-Breast Cancer Link

Twins provide breast cancer clues

Early Puberty Linked to Breast Cancer

July 15, 2003

Last updated July 23, 2006