Staging of breast cancer and survival rates.

To the Editor.— We read the article by Ferguson and associates in the Sept 17 issue entitled "Staging of Breast Cancer and Survival Rates" (1982;248:1337). The authors are to be congratulated for providing us with valuable information in this difficult area of evaluating the long-term effects of breast cancer. However, we must question the use of relative survival rates to determine the long-range effects of breast cancer. The relative survival rate at time X is given by the following equation: Probability of Surviving in Study Population to Time X/ Probability of Surviving in Control Population to Time X This ratio is then the proportion of the population escaping the excess (not absolute) risk of death caused by breast cancer if the risk of death by other causes is equal in both the study and the general population. It is known that patients from higher socioeconomic conditions have lower death rates