Breast Cancer's Genetic Profile

Researchers have found a genetic signature in breast tumors that seems to be a powerful predictor of whether the cancer will spread and kill or whether it can easily be cured by surgery, causing no further harm. The genetic signature—the activity of a collection of 70 genes—appears to predict cancer mortality better than traditional measures like tumor size, stage or number of positive nodes. In the study, 5.5% of women with “good” genetic signatures died within 10 years, while 45% of women with “bad” signatures died in that period.

Doctors have long asssumed that small cancers were more treatable; that as the tumor grows, it acquires mutations that enable it to spread throughout the body. This study indicates that tumor size may be unimportant, that most tumors appear to be potentially deadly from the very start. Doctors also assumed that after surgery, cancer patients should be treated with a combination of chemotherapy, hormone therapy, and radiation, based on the belief that it is very difficult to differentiate women who will be helped by additional treatment from those who do not need it. The hope is that we may soon be able to identify subsets of patients who require less aggressive therapy or no therapy at all.

The women whose cancer cells indicated a good prognosis had an 85.2% chance of remaining free of cancer over the next decade and a 94.5% chance of surviving the decade. Those who cancer cells indicated a poor prognosis had a 50.% chance of remaining cancer-free and a 54.6% chance of surviving the decade. Small tumors often had a bad genetic signature while large tumors often had good ones, throwing into question a common assumption about how cancers develop. This notion is that tumors go through an evolution where they acquire more mutations as they grow bigger, and that small tumors are inherently less aggressive and less malignant. This is not to say that a small and harmless cancer can never mutate to become deadly, but rather that most deadly cancers are potentially life-threatening even when they are very small.

Metastatic potential may be hard-wired at the time of diagnosis, size, per se, may not matter that much.