An unexpected diagnosis in a patient with new-onset pulmonary infiltrates during adjuvant therapy for breast cancer.

The differential diagnosis of new-onset pulmonary infiltrates during adjuvant therapy in a cancer patient is challenging. Opportunistic infections, pulmonary drug-induced toxicity and metastatic dissemination of the underlying cancer are the most common causes. However, although infrequent, the development of a second primary pulmonary neoplasia should be taken into account. We present the clinical case of a breast cancer patient who developed progressive pulmonary infiltrates during adjuvant therapy, who was finally diagnosed as having a second lung neoplasm of unexpected histology.