Tumor Response Assessment to Treatment with [177Lu-DOTA0,Tyr3]Octreotate in Patients with Gastroenteropancreatic and Bronchial Neuroendocrine Tumors: Differential Response of Bone Versus Soft-Tissue Lesions

Abstract

We have noted that bone lesions on CT respond differently from soft-tissue lesions to treatment with [(177)Lu-DOTA(0),Tyr(3)]octreotate ((177)Lu-octreotate). We therefore compared the response of bone lesions with that of soft-tissue lesions to treatment with (177)Lu-octreotate in patients with gastroenteropancreatic and bronchial neuroendocrine tumors (NETs). Forty-two patients with well-differentiated NETs who had bone metastases that were positive on [(111)In-DTPA(0)]octreotide somatostatin receptor scintigraphy (SRS) before treatment, and who had soft-tissue lesions, were studied. All patients had had a minimum of 1 follow-up CT scan. Lesions were scored on CT and bone lesions also on SRS before and after treatment. Tumor markers (chromogranin A and 5-hydroxyindoleacetic acid) before and after treatment were compared. Because bone lesions were not visible on CT before treatment in 11 of 42 patients (26%), bone and soft-tissue lesions were evaluated in 31 patients. Whereas bone lesions increased in size, soft-tissue lesions decreased in size. The percentage change in bone and soft-tissue lesions was significantly different at all time points up to 12 mo of follow-up (P < 0.001). The intensity or number of bone lesions on SRS decreased after treatment in 19 of 23 patients (83%) in whom SRS after treatment was available. The tumor markers also decreased significantly after treatment. In 1 patient, bone lesions became visible on CT after treatment, mimicking progressive disease with "new" bone lesions, although there was an overall treatment response. In patients with NETs, the apparent increase in size of bone lesions or the appearance of new bone lesions on CT after treatment with (177)Lu-octreotate should be interpreted cautiously, as this finding may be therapy-related rather than indicative of tumor progression.