Gains of chromosome 8 are confined to mesenchymal components in pleuropulmonary blastoma

Pleuropulmonary blastoma, an aggressive tumor that is emerging as a distinc t entity of childhood, is characterized by mesenchymal elements (including undifferentiated blastema and often cartilaginous, rhabdomyoblastic, or fib roblastic differentiation) and epithelium-lined spaces. We investigated two patients with pleuropulmonary blastoma, a 3-year-old boy and an 11-year-ol d girl, both with large cystic masses replacing one lung. In both children, the post-chemotherapy resection specimens showed more maturation of rhabdo myoblasts and more nuclear pleomorphism in all mesenchymal cell lines, comp ared with biopsies sampled before treatment. Karyotypic analysis demonstrat ed gains in chromosome 8 in both cases and 17p deletion in one case. Fluore scent in situ hybridization analysis demonstrated that the chromosome 8 gai ns were present in all mesenchymal elements, including undifferentiated bla stematous, rhabdomyoblastic, fibroblastic, and chondroblastic areas. Epithe lial cells showed no chromosome 8 gains. The chromosome 8 aberrations were not appreciably different in pre- versus post-chemotherapy tissue. Our find ings substantiate previous reports that polysomy of chromosome 8 is a consi stent feature of pleuropulmonary blastoma. Further, they indicate that clon al proliferation in pleuropulmonary blastoma is restricted to the malignant mesenchymal elements, supporting the notion that the epithelial components of this tumor are non-neoplastic.