With the medical value of mammograms at any age called into question by a massive study published Tuesday, what's a woman to do? The best advice is the most basic: Ask a doctor familiar with your medical and family history what's best for you.

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The study followed 90,000 women for 25 years. Some had regular mammograms and breast exams, others breast exams alone. Death rates from breast cancer and other causes were the same for each group. And one in five cancers detected by mammograms and treated were not a threat. Prestigious groups, including the American Cancer Society and the U.S. Preventive Services Task Force, disagree on the age women should start having mammograms and how often they should be done.

What is clear: There is no standard guideline that can be recommended for all.