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Breast cancer has traditionally been thought of as a disease of midlife and beyond, with risk climbing steadily as women age. Over the past couple of decades, though, cancer registries in multiple countries have documented a genuine increase in breast cancer diagnoses among women under 50, and in some analyses, under 40, a trend that has prompted considerable research attention and, understandably, concern among younger women themselves.
This trend does not have a single confirmed explanation, and researchers are actively studying several contributing factors simultaneously rather than pointing to one clear cause. Understanding the leading hypotheses helps put the trend in context without overstating certainty about any one explanation.
