IMPORTANCE Disseminated retinoblastoma is usually fatal. Identification of small amounts (minimal dissemination [MD]) of tumor cells in extraocular sites might be a tool for designing appropriate treatments. OBJECTIVE To test cone-rod homeobox (CRX) transcription factor as a lineage-specific molecular marker for metastatic retinoblastoma and for evaluation of MD. DESIGN, SETTING, AND PARTICIPANTS In a prospective cohort design study, we evaluated CRX messenger RNA (mRNA) by retrotranscription followed by real-time polymerase chain reaction as a diagnostic test in samples obtained from bone marrow, peripheral blood, and cerebrospinal fluid (CSF) at diagnosis, after induction chemotherapy, and during follow-up. The study was conducted from June 30, 2008, to June 30, 2014. Seventeen retinoblastoma primary tumors, 2 retinoblastoma cell lines, and 47 samples of bone marrow from other cancers (controls) were studied. Seventeen patients with metastatic retinoblastoma (9 at diagnosis, 8 at relapse; age range: 18-41 months) were included. MAIN OUTCOMES AND MEASURES Detection of CRX mRNA as a marker for metastatic retinoblastoma and MD in bone marrow and CSF and its correlation with clinical findings. RESULTS Cone-rod homeobox mRNA was expressed in all tumors (relative expression levels range, 8.1 × 10 −5 to 5.6) and cell lines. In control samples, there was no amplification of CRX; only the housekeeping gene (GAPDH) demonstrated amplification. Bone marrow metastatic cells showed expression of CRX mRNA in all 9 children presenting with metastasis at the diagnosis (relative expression levels, 6.0 × 10 −5 to 0.67). After induction chemotherapy, no evidence of MD of tumor cells was seen in any of the 8 responding children since only GAPDH showed amplification. In the CSF of children who had a metastatic relapse, CRX mRNA detection was positive in 2 patients in whom no conclusive results were reached by immunocytology for disialoganglioside GD2. Minimal dissemination in the CSF was associated with a clinical relapse in 2 cases. No concomitant MD was evident in the bone marrow in any case. CONCLUSIONS AND RELEVANCE These data suggest that CRX mRNA is a novel marker for retinoblastoma at extraocular sites. In this study among patients with bone marrow metastasis, there was a quick, complete, and sustained molecular response after induction chemotherapy. In all patients with secondary metastasis, CSF relapse occurred independently from the bone marrow, suggesting a sanctuary site.

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IMPORTANCE Fatal metastatic relapse may occur in children with retinoblastoma and high-risk pathologic features (HRPFs). Minimal dissemination (MD) may be an additional tool for risk estimation. The use of cone-rod homeobox (CRX) transcription factor messenger RNA for MD evaluation in metastatic retinoblastoma was previously reported, but no data in nonmetastatic cases with HRPFs are available. OBJECTIVES To evaluate whether MD is detectable in patients with nonmetastatic retinoblastoma and to assess its prognostic effect on disease-free survival (DFS). DESIGN, SETTING, AND PARTICIPANTS This single-institution cohort study of patients with nonmetastatic retinoblastoma and HRPFs used prospectively defined inclusion criteria and a sampling strategy to procure bone marrow (BM) and cerebrospinal fluid (CSF) samples from May 1, 2007, through October 31, 2013. Median follow-up was 38 months (range, 8-89 months). Survival analysis was closed in December 2015, and no further updates were made after that point. INTERVENTIONS The study evaluated CRX messenger RNA by quantitative polymerase chain reaction in BM and CSF at diagnosis and follow-up. In 14 patients, GD2 synthase was used instead of CRX for CSF evaluation. Patients were treated under uniform guidelines. MAIN OUTCOMES AND MEASURES Metastatic relapse. RESULTS The study included 96 children (median age at study inclusion, 26 months; range, 1-168 months; 46 male [47.9%]; 50 female [52.1%]) with nonmetastatic retinoblastoma and HRPFs (isolated massive choroidal invasion in 14, postlaminar optic nerve invasion in 51 [26 with concomitant massive choroidal and 13 with scleral invasion], 12 with scleral invasion without postlaminar optic nerve invasion, and 7 with tumor at the resection margin of the optic nerve) were evaluated at the time of primary or secondary enucleation. Minimal dissemination was detected in 9 patients (7 BM samples and 2 CSF samples) and was associated with extension beyond the resection margin of the optic nerve and scleral involvement, but only the former was independently associated (adjusted odds ratio, 57.0; 95% CI, 4.8-678.2; P = .001). In addition, MD occurred in 8 of the 43 International Intraocular Retinoblastoma Classification group E eyes with glaucoma (18.6%) and in 8 of 80 (10%) and 1 of 16 children (6.3%) who underwent primary or secondary enucleation, respectively. Children with MD had a 3-year DFS of 0.78 compared with 0.98 in those without MD (95% CI for the difference in DFS, 0.17-0.23; P = .004). CONCLUSIONS AND RELEVANCE These findings identified a high-risk population of children with retinoblastoma and HRPFs with MD. Because the number of events was small, these results, which suggest that children with International Intraocular Retinoblastoma Classification group E retinoblastoma and glaucoma have a higher risk of MD at diagnosis, should not be considered definitive at this time.

Current treatment of retinoblastoma involves using the maximum dose of chemotherapy that induces tumor control and is tolerated by patients. The impact of dose and schedule on the cytotoxicity of chemotherapy has not been studied. Our aim was to gain insight into the cytotoxic and antiangiogenic effect of the treatment scheme of chemotherapy used in retinoblastoma by means of different in vitro models and to evaluate potential effects on multi-drug resistance proteins. Two commercial and two patient-derived retinoblastoma cell types and two human vascular endothelial cell types were exposed to increasing concentrations of melphalan or topotecan in a conventional (single exposure) or metronomic (7-day continuous exposure) treatment scheme. The concentration of chemotherapy causing a 50% decrease in cell proliferation (IC50) was determined by MTT and induction of apoptosis was evaluated by flow cytometry. Expression of ABCB1, ABCG2 and ABCC1 after conventional or metronomic treatments was assessed by RT-qPCR. We also evaluated the in vivo response to conventional (0.6 mg/kg once a week for 2 weeks) and metronomic (5 days a week for 2 weeks) topotecan in a retinoblastoma xenograft model. Melphalan and topotecan were cytotoxic to both retinoblastoma and endothelial cells after conventional and metronomic treatments. A significant decrease in the IC50 (median, 13-fold; range: 3–23) was observed following metronomic chemotherapy treatment in retinoblastoma and endothelial cell types compared to conventional treatment (p<0.05). Metronomic topotecan or melphalan significantly inhibited in vitro tube formation in HUVEC and EPC compared to vehicle-treated cells (p<0.05). Both treatment schemes induced apoptosis and/or necrosis in all cell models. No significant difference was observed in the expression of ABCB1, ABCC1 or ABCG2 when comparing cells treated with melphalan or topotecan between treatment schedules at the IC50 or with control cells (p>0.05). In mice, continuous topotecan lead to significantly lower tumor volumes compared to conventional treatment after 14 days of treatment (p<0.05). Continuous exposure to melphalan or topotecan increased the chemosensitivity of retinoblastoma and endothelial cells to both chemotherapy agents with lower IC50 values compared to short-term treatment. These findings were validated in an in vivo model. None of the dosing modalities induced multidrug resistance mechanisms while apoptosis was the mechanism of cell death after both treatment schedules. Metronomic chemotherapy may be a valid option for retinoblastoma treatment allowing reductions of the daily dose.

Digoxin has antitumor activity for retinoblastoma while exerting antiangiogenic activity in vitro at similar concentrations. Metronomic treatment showed no advantage in terms of dose for cytotoxic effect. Four biweekly injections of digoxin led to local toxicity to the retina but no systemic toxicity in rabbits.