Expression of PD‐1/PD‐L1 in children's classical Hodgkin lymphomas

Abstract Background Although a prognosis of recurrent or refractory childhood Hodgkin lymphoma (HL) is associated with poor outcomes despite intensive therapy, the immune checkpoint inhibitors PD‐1/PD‐L1 appear to be therapeutic alternatives for advanced adult cases. However, these pharmacotherapies are yet to be studied in a pediatric population. Procedure The present study measured the expression of PD‐1/PD‐L1 in diagnostic samples of children with classical HL, according to the disease course. This study included two groups of patients treated at the Department of Pediatric Oncology, Bordeaux University Hospital—a group of cured or in‐remission cases and a group of relapsed or refractory cases. Immunohistochemical analyses of anti‐PD‐1 and anti‐PD‐L1 (clone 28‐8, companion test for nivolumab) were performed on baseline and follow‐up biopsies. Results Of the 42 included patients, 31 were cured or in remission and 11 were categorized as relapsed or refractory. At the time of diagnosis, PD‐1 expression was low (1‐3% of intratumoral lymphocytes labeled) in <20% of cases, whereas PD‐L1 was expressed by tumor cells in all cases, and strongly (≥50%) in most cases. There were no significant differences in the expression levels of the two checkpoint molecules between the groups. Initial biopsies showed strong expression of PD‐L1, whereas expression of PD‐1 was rare. Conclusions The identical labeling profiles of the cured and relapsed/refractory patients suggest that comparable responses to inhibitors of the PD1/PDL1 immunological checkpoints could be expected in patients undergoing first‐, second‐, or third‐line therapy.