THE ISSUE: Experts have wondered whether improved breast cancer survival is due to better treatment or to spotting tumors earlier.

WHAT’S NEW: Cancer records over 25 years show that the average size of tumors at diagnosis is much smaller today, compared to previous years, accounting for much of the improvement in survival.

THE IMPLICATIONS: Mammograms are helping find tumors sooner, and smaller tumors are resulting in fewer deaths from breast cancer.

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