Atypical hyperplasia is a condition where cells in a tissue grow abnormally but are not cancerous. This growth can occur in various tissues, most commonly in the breast and endometrium (the lining of the uterus). Atypical hyperplasia is often considered a marker for an increased risk of developing cancer in the future, prompting closer monitoring and sometimes preventive measures. Diagnosis typically involves a biopsy, where a sample of tissue is examined under a microscope. If atypical hyperplasia is detected, healthcare providers may recommend regular screenings or additional tests to ensure any potential progression to cancer is caught early.