Targeted therapies in retinoblastoma: GD2-directed immunotherapy following autologous stem cell transplantation and evaluation of alternative target B7-H3.

BACKGROUND: GD2-directed immunotherapy is highly effective in the treatment of high-risk neuroblastoma (NB), and might be an interesting target also in other high-risk tumors. METHODS: The German-Austrian Retinoblastoma Registry, Essen, was searched for patients, who were treated with anti-GD2 monoclonal antibody (mAb) dinutuximab beta (Db) in order to evaluate toxicity, response and outcome in these patients. Additionally, we evaluated anti-GD2 antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) in retinoblastoma cell lines in vitro. Furthermore, in vitro cytotoxicity assays directed against B7-H3 (CD276), a new identified potential target in RB, were performed. RESULTS: We identified four patients with relapsed stage IV retinoblastoma, who were treated with Db following autologous stem cell transplantation (ASCT). Two out of two evaluable patients with detectable tumors responded to immunotherapy. One of these and another patient who received immunotherapy without residual disease relapsed 10 and 12 months after start of Db. The other patients remained in remission until last follow-up 26 and 45 months, respectively. In vitro, significant lysis of RB cell lines by ADCC and CDC with samples from patients and healthy donors and anti-GD2 and anti-CD276-mAbs were demonstrated. CONCLUSION: Anti-GD2-directed immunotherapy represents an additional therapeutic option in high-risk metastasized RB. Moreover, CD276 is another target of interest.

Introduction of a Variant Classification System for Analysis of Genotype-Phenotype Relationships in Heritable Retinoblastoma.

Constitutional haploinsufficiency of the RB1 gene causes heritable retinoblastoma, a tumor predisposition syndrome. Patients with heritable retinoblastoma develop multiple retinoblastomas early in childhood and other extraocular tumors later in life. Constitutional pathogenic variants in RB1 are heterogeneous, and a few genotype-phenotype correlations have been described. To identify further genotype-phenotype relationships, we developed the retinoblastoma variant effect classification (REC), which considers each variant's predicted effects on the common causal mediator, RB1 protein pRB. For validation, the RB1 variants of 287 patients were grouped according to REC. Multiple aspects of phenotypic expression were analyzed, known genotype-phenotype associations were revised, and new relationships were explored. Phenotypic expression of patients with REC-I, -II, and -III was distinct. Remarkably, the phenotype of patients with variants causing residual amounts of truncated pRB (REC-I) was more severe than patients with complete loss of RB1 (REC-II). The age of diagnosis of REC-I variants appeared to be distinct depending on truncation's localization relative to pRB structure domains. REC classes identify genotype-phenotype relationships and, therefore, this classification framework may serve as a tool to develop tailored tumor screening programs depending on the type of RB1 variant.

The impact of RB1 genotype on incidence of second tumours in heritable retinoblastoma.

BACKGROUND: Patients with heritable retinoblastoma are at risk for bilateral retinoblastoma and second primary malignancies (SPMs). The incidence of SPM is significantly raised after radiotherapy. We analysed the impact of the class of constitutional RB1 variant on the incidence of SPM in survivors with and without previous radiotherapy. METHODS: From 1940 to 2008, 655 national patients were treated for heritable retinoblastoma at the German referral centre. Data on SPM, therapy and constitutional RB1 variant were available for 317 patients (48.3%). Heterozygous RB1 variants were classified into variants with regular and incomplete penetrance for retinoblastoma. RESULTS: SPM occurred in 51 of 317 survivors of heritable retinoblastoma. The incidence rate (IR) of SPM per 1000 person years was 8.4 (95% confidence interval (CI): 6.3-11.1) in individuals heterozygous for an oncogenic RB1 variant and 2.1 (95% CI: 0.0-11.4) with RB1 mosaicism. The incidence of SPM was higher in patients with regular penetrance compared with incomplete penetrance RB1 variants (IR 10.3 [95% CI: 7.5-13.8] vs. IR 3.2 [95% CI: 1.0-7.5]; p < 0.05). In the subgroup without previous radiotherapy SPM were only observed in patients with regular penetrance variants (IR 6.3 [95% CI: 3.0-11.5]). Carriers of incomplete penetrance variants developed similar tumour entities as those with regular penetrance. CONCLUSIONS: Patients heterozygous for regular penetrance RB1 variants had a higher risk to develop SPM than patients with incomplete penetrance variants. Increased knowledge on genotype-phenotype relation regarding SPM may influence screening recommendations for SPM in survivors of heritable retinoblastoma.