Avelumab in Combination With Gemcitabine in Advanced Leiomyosarcoma as a Second-line Treatment

Inclusion Criteria: 1. Unresectable, advanced or metastatic histologically confirmed leiomyosarcoma 2. Progression during or after first-line doxorubicin-based chemotherapy (relapse within 6 months of completion of adjuvant/neoadjuvant chemotherapy containing doxorubicin-based regimen could be considered as first-line therapy.) 3. ECOG PS 0-2 4. At least one measurable lesion according to RECIST v1.1 5. Adequate organ function 6. Life expectancy \>= 3 months 7. Negative serum or urine pregnancy test at screening for women of childbearing potential Exclusion Criteria: 1. Prior treatment history of anti-PD-1/PD-L1 or anti-CTLA4 treatment 2. Receipt of 2 or more prior systemic treatments for advanced leiomyosarcoma 3. Active or untreated brain metastases or spinal cord compression 4. Prior treatment with gemcitabine 5. History of major surgery within 4 weeks prior to enrollment 6. Chemotherapy or radiotherapy within 3 weeks prior to the study drug commencement 7. Previous malignant disease other than leiomyosarcoma within the last 5 years with the exception of basal or squamous cell carcinoma of skin or carcinoma in situ (bladder, cervical, colorectal, breast) 8. Pregnant or lactating women 9. HIV, HBV, or HCV infection 10. Severe hypersensitivity or anaphylaxis to monoclonal antibody, or uncontrolled bronchial asthma 11. Current use of immunosuppressive agent (exclusion : less than prednisone 10 mg/day or equivalent) 12. Active autoimmune disease 13. Clinically significant cardiovascular disease 14. Clinically significant interstitial pneumonitis or pulmonary fibrosis 15. Vaccination within 4 weeks of the first dose of avelumab and while on trial is prohibited except for administration of inactivated vaccines