Health Insurance Plan (HIP) of Greater New York mammography trial

By the mid-1960s, breast cancer was the leading cause of cancer death in American women, yet there was no evidence that finding tumors earlier actually reduced mortality. Observational studies had produced encouraging signals, but lead-time and length-time bias made them impossible to interpret. What was needed was a randomized trial with death, not detection, as the primary outcome.

Philip Strax, a radiologist whose own wife had died of breast cancer, approached the Health Insurance Plan of Greater New York with a proposal for exactly that trial. Working with surgeon Louis Venet and biostatistician Sam Shapiro, Strax recruited roughly 30,100 women aged 40 to 64 and offered them annual mammography combined with clinical breast examination; a matched group of about 30,600 women received usual care with no additional screening. The study launched in 1963, and Strax, Shapiro, and Venet published their principal mortality results in JAMA in 1971.

After roughly seven years of follow-up, breast cancer mortality in the screened group was approximately 30 percent lower than in controls, with the reduction concentrated in women over 50. The finding was not subtle enough to attribute to chance, and it answered the core methodological objection: this was a randomized trial with mortality as the endpoint, not a case series of stage distributions. Earlier detection, in at least some women, was translating into fewer deaths.

Criticism of the trial was substantive and persisted for decades. The intervention combined mammography and physical examination, so the independent contribution of mammography alone could not be isolated. The equipment used was far inferior to later technology, and compliance was incomplete. A sizable proportion of women in the control group eventually obtained mammography on their own, diluting the between-group difference. These limitations left the HIP results suggestive but not conclusive, and they shaped the design of subsequent Swedish and British trials.

Despite those caveats, the HIP data provided the primary evidence base for the earliest U.S. recommendations to offer routine mammography screening. The American Cancer Society began recommending screening mammography in the 1970s partly on the strength of this trial. Later Scandinavian trials confirmed mortality reductions in older women, though guidelines still disagree on the size of the benefit and the right age to start screening.