Some randomized studies are conducted at single centers, while others are conducted at diverse sites (that is, multiple centers). Almost 2,500 node-negative breast cancer patients were enrolled and treated in these randomized studies. Using these adjustments, we found that, on average, similar patient survival followed the two treatments. Thus, the adjusted survival rates are based on “matched” treatment groups; that is, the kinds of patients who were unlikely to receive breast-conservation therapy contribute equally to the breast- conservation and the mastectomy survival estimates—as do the kinds of patients who were much more likely to receive breast- conservation therapy. Logically, the SEER combined-treatments survival rate is not affected by internal selection bias. From table 11, it is clear that with breast-conservation and mastectomy patients taken together, the 5-year survival rate for patients in single-center randomized studies is higher than the rate for the corresponding SEER estimate—by a difference of 4.3 percentage points, which is statistically significant. We recognize that database analyses are vulnerable to hidden selection bias. Only one caveat was suggested by the results of our analyses: A minority of breast-conservation patients—the kinds of patients for whom breast-conservation therapy was relatively unlikely to be used (based on factors such as residence in areas where breast-conservation is relatively uncommon) but who nevertheless did receive it—may have achieved slightly better results with mastectomy. Asian women had lower odds than others of receiving breast-conservation therapy, although they may have somewhat better prognoses than other breast cancer patients. GAO. No.
Why GAO Did This Study

Pursuant to a congressional request, GAO reviewed the survival rates of patients receiving breast-conservation therapy versus mastectomy therapy, focusing on whether patients' survivability is affected by having treatment in single-center studies rather than multi-center studies.

What GAO Found

GAO found that: (1) the 5-year survival rates for breast cancer patients treated with breast-conservation therapy were similar to that of mastectomy in community medical practices; (2) patients that were treated at single-center facilities usually had slightly higher survivability rates than patients who received treatment at multi-center facilities; (3) on average, breast cancer patients appear to be at no appreciable risk by selecting breast-conservation therapy rather than mastectomy; (4) although patient survivability data were vulnerable to hidden selection bias, such bias was unlikely since the group of patients reviewed were homogeneous and adjustments were made for patients' health and demographic characteristics; and (5) although a minority of patients who voluntarily chose breast-conservation therapy over recommended mastectomy therapy could have achieved slightly better results with mastectomy, the differences were not statistically significant.