2761 - Pain Outcomes and Survival after Radiotherapy for Malignant Psoas Syndrome: A Multicenter Cohort
Presenter(s)
Y. Ishikawa1, K. Makita2, Y. Wada3, T. Fujisawa4, Y. Hiroshima2, M. Wakabayashi2, and T. Saito5; 1Tohoku Medical and Pharmaceutical University, Sendai, Japan, 2National Cancer Center Hospital East, Kashiwa, Japan, 3Akita University Graduate School of Medicine, Akita, Japan, 4University of Tsukuba, Tsukuba, Japan, 5Division of Integrative Medical Oncology, Saiseikai Kumamoto Hospital, Kumamoto, Japan
Purpose/Objective(s): Malignant psoas syndrome (MPS) is a rare cancer-related pain syndrome caused by malignant infiltration of the iliopsoas muscle. Evidence regarding outcomes after conventional palliative radiotherapy (pRT) is limited. We evaluated pain response to pRT in patients with MPS secondary to non-osseous metastases and described overall survival (OS) in the entire treated cohort.
Materials/Methods: We retrospectively analyzed consecutive patients with MPS treated with radiotherapy at four institutions between 2013 and 2025. Prescribed doses for the overall cohort ranged from 4 to 66 Gy (median, 30 Gy). OS was estimated using the Kaplan–Meier method. For pain-response analysis, we included patients with MPS secondary to non-osseous metastases who received pRT =30 Gy (median, 20 Gy). Pain response was assessed at 1, 2, 4, and 8 weeks using modified International Consensus Endpoints incorporating pain score and oral morphine equivalent dose. Complete and partial responses were defined as overall response. Patients who died within 4 weeks were considered non-evaluable.
Results: Ninety-seven patients were treated (median age, 69 years [range, 5–89]). Fifty-seven were male (59%) and 40 were female (41%). Primary tumor sites included gastrointestinal (31%), genitourinary (27%), gynecologic (9%), lung (7%), and other primary sites (26%). Sixty-four patients died; median OS was 165 days (95% CI, 113–265). The median follow-up time was 113 days (interquartile range, 49–265 days). In the pRT =30 Gy cohort (n=54), the 56-day survival rate was 86.8%; 38 patients (70.4%) had died at the time of analysis. Overall response in evaluable patients was 61% (complete response, 24%; partial response, 37%), while 39% had no response. Of the responders, 91% achieved response within 4 weeks. Exploratory analyses showed no significant association between response and fractionation, tumor burden, baseline pain, or opioid dose (all p > 0.05). No grade =2 treatment-related adverse events were observed in this cohort.
Conclusion: In this multicenter retrospective analysis, MPS was associated with limited survival. pRT =30 Gy was associated with meaningful pain relief in more than half of evaluable patients, typically within 4 weeks. This treatment may represent a palliative option for MPS.