When it comes to deciding on treatment options with breast cancer (or any other disease) it can get hugely confusing to understand the various statistics in favor of one treatment or another. Steve Kass, an old high-school buddy who now happens to be a professor of mathematics has some thoughtful observations about looking at survival rates and death rates when it comes to breast cancer:
The five-year death rate after mastectomy was 11.5% for women who had both breasts removed. It was 16.3% for those who only had the cancerous breast removed. Adding a contralateral prophylactic mastectomy to the original surgery therefore reduced the five-year death rate from 16.3% to 11.5%. Almost a third fewer mastectomy patients died within 5 years when they had chosen to remove the second (healthy) breast, compared to mastectomy patients who had not chosen to remove the second breast. The bilateral mastectomy decreased the 5-year death rate by 29.4%.
This strikes me as a significant benefit. Suppose I have breast cancer and need a mastectomy. I can choose a single mastectomy and have a one-in-6 chance of dying in five years, or I can choose a double mastectomy and have a one-in-9 chance of dying in five years. One-in-9 sounds quite a bit better to me. If 100,000 women with unilateral cancer need mastectomies, performing 100,000 double mastectomies instead of 100,000 unilateral mastectomies will reduce the number of deaths in the first five years from 16,300 to 11,500. About 4,800 fewer women will die within five years.
The reporting of this study takes a very different viewpoint. It compares the survival rate, not the death rate, and notes that the bilateral prophylactic mastectomy increases the survival rate from 83.7% to 88.5%, “a difference of less than 5%.” Five percent sounds like a small number, but 5,000 lives saved sounds like a large number.
Both statements (lowers by 30%; benefits only 5%) are the same. Only the intent to communicate is different.
The full post is well worth the read. Being a strong believer in having as much information as possible when facing difficult decisions, thought this was worth passing along. Also of note, this New York Times blog piece regarding women choosing bilateral mastectomies even when it does not improve their chances for survival.