[Three cases of second primary lung cancer after radiotherapy for breast cancer].

We report three cases of primary lung cancer after radiotherapy for breast cancer. Case 1 was a 73-year-old woman, who had bilateral breast cancer 27 years previously. Case 2 was a 70-year-old woman, who had left breast cancer 31 years previously. Case 3 was a 56-year-old woman, who had left breast cancer 14 years previously. Since all three lung cancers developed within the irradiated field, breast cancer radiotherapy was speculated to be one of the contributing factors for their lung cancers. Clinicians treating breast cancer survivors who have received Cobalt-60 radiation therapy and are or have been smokers should be aware of the risk of lung cancer over 10 years or more after radiotherapy.