Breast cancer in young identical twins

A 25 year old presented with a 12-week history of a mobile breast lump. Mammography and breast ultrasound demonstrated a 3 cm mass lesion, extensive microcalcification and axillary lymphadenopathy. Core biopsies confirmed a grade 3 ductal carcinoma and high-grade ductal carcinoma in situ.

Several weeks later her identical twin sister attended the family history breast cancer clinic. Clinical breast examination was normal but, despite the patient's age, it was decided to carry out a baseline mammogram. This showed widespread casting microcalcification, and core biopsies confirmed extensive high-grade ductal carcinoma in situ.

When one twin has breast cancer, one-third of identical twins develop breast cancer at some time in their lives. Nonidentical twins of breast cancer patients have a much smaller risk of the disease. This suggests identical twins gain their increased risk by inheriting the same set of genes as their sister with cancer, rather than through sharing the womb or being brought up together. Where one twin develops breast cancer at an early age, the other has a high chance of doing likewise.