SUMMARY Background Sodium thiosulfate (STS) is an antioxidant shown in preclinical studies to prevent cisplatin-induced hearing loss (CIHL) but not compromise anti-tumour efficacy with timed administration post-cisplatin. The primary study aim was to evaluate STS for prevention of CIHL. Methods ACCL0431 was an open-label, phase 3 randomised cooperative group trial. Eligible participants 1–18 years old with newly diagnosed cancer and normal audiometry were randomly allocated (1:1) to receive STS or not in addition to their planned cisplatin-containing chemotherapy regimen using permuted blocks of 4. Randomisation was initially stratified by age (< or ≥ 5 years) and duration of cisplatin infusion (< or ≥ 2 hours). Stratification by prior cranial irradiation was added later. Sequence was computer-generated centrally and concealed to all personnel. If allocated to STS, participants received STS 16 grams/m2 intravenously 6 hours after each cisplatin dose. Hearing was measured using standard audiometry and reviewed centrally by audiologists masked to allocation using American Speech-Language-Hearing Association criteria. The primary endpoint was incidence of hearing loss 4 weeks post final cisplatin dose. Analysis was by intention to treat and restricted to evaluable participants. Enrollment is complete and this report represents the final analysis. This trial is registered with ClinicalTrials.gov, number NCT00716976. Findings Between June 23, 2008 and September 28, 2012, 125 eligible participants were enrolled from 38 sites in the United States (US) and Canada. Of these, 104 were evaluable for the primary aim. The proportion with hearing loss for STS versus control (%, 95% confidence interval) was 14/49 (28.6%, 16.6, 43.3) and 31/55 (56.4%, 42.3, 69.7), respectively (p=0.00022). Adjusted for stratification variables, the likelihood of hearing loss was significantly lower in the STS group compared with control group (odds ratio 0.31, 95% confidence interval 0.13, 0.73; p=0.0036). The most common grade 3–4 haematological adverse events (AE) reported in STS and control participants, irrespective of attribution, were neutropaenia in 117/177 (66.1%) and 145/223 (65.0%) participant-cycles, while the most common non-haematological AE was hypokalaemia in 25/147 (17.0%) and 22/187 (11.8%) participant-cycles, respectively. Of 194 serious AEs reported in STS recipients, none were considered probably or definitely related to STS; the most common was neutrophil count decreased in 26/194 (13.4%). Interpretation STS protects against CIHL in children and is not associated with serious adverse events attributed to its use. Further research is needed to define the appropriate role for STS among emerging otoprotection strategies. Funding United States NCI; STS was provided at no cost by Fennec Pharmaceuticals.

Purpose Constitutional mismatch repair deficiency (CMMRD) is a highly penetrant cancer predisposition syndrome caused by biallelic mutations in mismatch repair (MMR) genes. As several cancer syndromes are clinically similar, accurate diagnosis is critical to cancer screening and treatment. As genetic diagnosis is confounded by 15 or more pseudogenes and variants of uncertain significance, a robust diagnostic assay is urgently needed. We sought to determine whether an assay that directly measures MMR activity could accurately diagnose CMMRD. Patients and Methods In vitro MMR activity was quantified using a 3′-nicked G-T mismatched DNA substrate, which requires MSH2-MSH6 and MLH1-PMS2 for repair. We quantified MMR activity from 20 Epstein-Barr virus–transformed lymphoblastoid cell lines from patients with confirmed CMMRD. We also tested 20 lymphoblastoid cell lines from patients who were suspected for CMMRD. We also characterized MMR activity from patients with neurofibromatosis type 1, Li-Fraumeni syndrome, polymerase proofreading-associated cancer syndrome, and Lynch syndrome. Results All CMMRD cell lines had low MMR activity (n = 20; mean, 4.14 ± 1.56%) relative to controls (n = 6; mean, 44.00 ± 8.65%; P < .001). Repair was restored by complementation with the missing protein, which confirmed MMR deficiency. All cases of patients with suspected CMMRD were accurately diagnosed. Individuals with Lynch syndrome (n = 28), neurofibromatosis type 1 (n = 5), Li-Fraumeni syndrome (n = 5), and polymerase proofreading-associated cancer syndrome (n = 3) had MMR activity that was comparable to controls. To accelerate testing, we measured MMR activity directly from fresh lymphocytes, which yielded results in 8 days. Conclusion On the basis of the current data set, the in vitro G-T repair assay was able to diagnose CMMRD with 100% specificity and sensitivity. Rapid diagnosis before surgery in non-neoplastic tissues could speed proper therapeutic management.

POLE mutations are a major cause of hypermutant cancers, yet questions remain regarding mechanisms of tumorigenesis, genotype–phenotype correlation, and therapeutic considerations. In this study, we establish mouse models harboring cancer-associated POLE mutations P286R and S459F, which cause rapid albeit distinct time to cancer initiation in vivo, independent of their exonuclease activity. Mouse and human correlates enabled novel stratification of POLE mutations into three groups based on clinical phenotype and mutagenicity. Cancers driven by these mutations displayed striking resemblance to the human ultrahypermutation and specific signatures. Furthermore, Pole-driven cancers exhibited a continuous and stochastic mutagenesis mechanism, resulting in intertumoral and intratumoral heterogeneity. Checkpoint blockade did not prevent Pole lymphomas, but rather likely promoted lymphomagenesis as observed in humans. These observations provide insights into the carcinogenesis of POLE-driven tumors and valuable information for genetic counseling, surveillance, and immunotherapy for patients. Significance: Two mouse models of polymerase exonuclease deficiency shed light on mechanisms of mutation accumulation and considerations for immunotherapy. See related commentary by Wisdom and Kirsch p. 5459

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Mesenchymal progenitor cell subpopulations are differentially sensitive to radiation. Amifostine protects both mesenchymal and hematopoietic progenitors against radiation injury, though the level of protection appears to be dependent upon the sensitivities of these progenitor cells to radiation. Amifostine is a potent stimulant of BFU-E and CFU-GEMM progenitor colonies.