Suppression of UV-induced erythema by topical treatment with melatonin. Influence of the application time point.

B-cell lymphomas involving Waldeyer's ring (WR) comprise heterogeneous histolopathological subtypes with a wide age range and distinctive clinical features. However, the comparison between pediatric and adult patients is scarce and limited in the literature. Thirty-three cases of B-cell lymphomas involving WR, were collected and evaluated by histolopathological, immunohistochemical and FISH analyses. The 33 cases were categorized into children and adolescents referred as pediatric group (n = 12), aged (3-19) years and the adult group (n = 21), aged (20-84) years. The pediatric group included Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL) and MUM1-positive-lymphoma in 7, 3 and 2 cases, respectively. While the adult cases comprised of DLBCL, follicular lymphoma, and mucosa associated lymphoid tissue (MALT) lymphoma in 18, 2 and 1 case, respectively. Male gender was predominant in both groups with 3 folds frequency in the pediatric cases compared to 2 folds in the adults counterpart. Pediatric cases showed a significantly higher frequency of stage I disease (P = 0.019), germinal center B-cell (GCB) phenotype (P = 0.011), CD10-positive expression (P = 0.003), and MYC breaks (P = 0.029) compared to adults. However, MUM1 positive expression was less frequently detected in pediatric patients than adults (P = 0.082). BCL2 rearrangement was undetectable in both pediatric and adult groups. On the other hand, adult group had the significantly higher proportion of DLBCL (P < 0.001), BCL2 expression (P = 0.027) and stage II disease (P = 0.047) compared to pediatric group.In conclusion, B-cell lymphomas involving WR presented with a wide age range, and evident variation in clinical features, histopathological subtypes and immunophenotypes between pediatric and adult age groups.