Isolated metastasis to a pulmonary hamartoma

Intrapulmonary hamartomas are the most common benign pulmonary neoplasm, and malignant degeneration is exceedingly rare. Only a minority produce symptoms, and their major clinical significance is their ability to simulate a malignant pulmonary neoplasm in radiologic studies. Here we report a case of apparently localized prostatic adenocarcinoma with isolated metastasis to an intrapulmonary hamartoma. The pulmonary lesion was identified during staging and was ultimately resected. Prostatic adenocarcinoma involved the hamartoma extensively but did not involve adjacent lung tissue. The hamartoma was otherwise typical with predominantly cartilaginous differentiation. The malignant glands within the hamartoma showed strong reactivity for prostate specific antigen, excluding the possibility of malignant change within the hamartoma. To our knowledge, metastasis to a pulmonary hamartoma has not been previously reported, and this case raises several issues. The pattern of tumor spread suggests an affinity of the tumor cells for the hamartoma. The known propensity of prostatic adenocarcinoma to metastasize to osseous sites might underlie its apparent tropism for the cartilaginous milieu of a pulmonary hamartoma. Accurate pathologic staging of this patient's prostatic adenocarcinoma prevented a needless radical prostatectomy, and complete cancer staging may require histologic examination of clinically typical pulmonary hamartomas.