In men who otherwise seem to have responded to chemotherapy for nonseminomatous germ cell tumors (NSGCTs), enlarging masses can represent benign tissue rather than residual or recurrent malignancy. One hundred eighty-five men with negative serum tumor markers after first-line chemotherapy for NSGCT underwent surgical resection of residual masses within 6 months after completing therapy. Radiologic examinations revealed 14 patients who had 17 masses (10 retroperitoneal, five pulmonary, two mediastinal) that had enlarged despite therapy. Fourteen (82%) of the masses were teratomas (13 mature, one immature), two (12%) were necrotic tissue, and one (6%) was a mature teratoma with sarcomatous transformation. All 12 retroperitoneal and mediastinal teratomatous masses were at least partially cystic at posttherapy computed tomography. Seven of the 14 patients had a differential response to therapy: Some masses regressed while others enlarged. Enlarging masses in patients with negative serum tumor markers after chemotherapy for NSGCT frequently represent mature teratomas. Complete surgical resection of such masses usually is curative and identifies patients with residual malignancy who require further therapy.
