Radiographic response of desmoplastic mesenteric lesions to peptide receptor radionuclide therapy (PRRT).

Abstract

362 Background: 177Lu-dotatate PRRT is indicated in well-differentiated, SSTR+ small bowel NETs. These tumors often metastasize to mesenteric lymph nodes and produce a desmoplastic reaction, consisting of tumor cells mixed with fibrotic tissue. We hypothesized that in patients treated with 177Lu-dotatate, mesenteric tumors would remain stable even as liver tumor size changes were observed. Methods: We retrospectively reviewed the records of all patients treated with 177Lu-dotatate between 4/2018 and 12/2019. Among patients with desmoplastic mesenteric tumors and liver metastases, we evaluated changes in tumor size of mesenteric and liver lesions based on pre and post-treatment radiology reports. Due to the infrequency of objective radiographic response (ORR), any reported changes in tumor size were considered significant. Scans were subsequently reviewed by a radiologist to confirm findings. Results: 21 patients met the inclusion criteria: 9 had evidence of shrinkage of liver lesion(s), 1 report described mild progression of liver lesions, 7 described stable hepatic disease and 4 described mixed hepatic progression/response. 2 of the patients with hepatic tumor shrinkage met criteria for PR by RECIST 1.1. Desmoplastic mesenteric lesions remained unchanged in size, regardless of the changes detected on liver lesions. Conclusions: 177Lu-dotatate does not impact desmoplastic mesenteric tumors typically associated with midgut NETs. Patients whose disease is confined to desmoplastic mesenteric lesions are unlikely to respond radiographically to PRRT. Moreover, the inclusion of desmoplastic mesenteric lesions as target lesions in RECIST measurements increases rates of disease stability versus response or progression.