Gynecologic Cancer Intergroup Symptom Benefit Study (GCIG-SBS) Stage 2 aimed to review, revise, and validate a patient-reported outcome measure (PROM), the Measure of Ovarian Symptoms and Treatment concerns (MOST), developed in GCIG-SBS Stage 1 (MOSTv1, 35 items), and document recurrent ovarian cancer (ROC) symptom burden and benefit. GCIG-SBS Stage 2 recruited patients with platinum-resistant/refractory ROC (PRR-ROC) or potentially platinum-sensitive ROC with aeamp;lt;yenamp;gt; 3 lines of prior chemotherapy (PPS-ROC aeamp;lt;yenamp;gt; 3). Patients completed MOSTv1, QLQ-C30, QLQ-OV28, and FACT-O/FOSI at baseline and before cycle 3 of chemotherapy (pre-C3), and global assessments of change (MOST-Change) pre-C3. Clinicians rated patients cancer-related symptoms, performance status, and adverse events. Convergent and divergent validity (Spearmans correlations), discriminative validity (effect sizes between groups classified by clinician-rated characteristics), and responsiveness (paired t tests in patients expected to experience clinically meaningful change) were assessed. Of 948 recruits, 903 completed PROMs at baseline and 685 pre-C3. Baseline symptom burden was substantial for PRR-ROC and PPS-ROC aeamp;lt;yenamp;gt; 3. MOSTv2 has 24 items and five multi-item scales: abdominal symptoms (MOST-Abdo), disease or treatment-related symptoms (MOST-DorT), chemotherapy-related symptoms (MOST-Chemo), psychological symptoms (MOST-Psych), and MOST-Well-being. Correlations confirmed concurrent and divergent validity. Discriminative validity was confirmed by effect sizes that conformed with a priori hypotheses. MOST-Abdo was responsive to improvements in abdominal symptoms and MOST-Chemo detected the adverse effects of chemotherapy. The MOSTv2 validly quantifies patient-reported symptom burden, adverse effects, and symptom benefit in ROC, and as such is fit-for-purpose for clinical trials of palliative chemotherapy in ROC. Further research is required to assess test-retest reliability.