Despite recent advances in ovarian cancer (OC) treatment, including the introduction of bevacizumab and PARP-inhibitors, OC remains a lethal disease. Other therapeutic options are being explored, such as immunotherapy (IT), which has been proved effective in many solid tumors. Findings about tumor-infiltrating cytotoxic and regulatory T cells, together with the expression of PD-1 on immune cells and of PD-L1 on tumor cells, gave the rationale for an attempt to the use of IT also in OC. We treated two patients with avelumab, an anti-PD-L1 monoclonal antibody, after the first line of chemotherapy: Patient A underwent 19 cycles of maintenance therapy with avelumab with a disease-free interval of 12 months, whereas patient B showed a slight progression of disease after only eight cycles. A higher PD-L1 expression in tumor cells of patient A was detected. She also underwent a genomic assessment that described the presence of a high Tumor Mutational Burden (TMB) and a status of Loss of Heterozygosity (LoH). This different response to the same treatment puts in evidence that some genomic and immune features might be investigated.