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IMPORTANCE: Spitz nevi are benign melanocytic neoplasms that classically present in childhood. Isolated Spitz nevi have been associated with oncogenic gene fusions in approximately 50% of cases. The rare agminated variant of Spitz nevi, thought to arise from cutaneous genetic mosaicism, is characterized by development of clusters of multiple lesions in a segmental distribution, which can complicate surgical removal. Somatic single-nucleotide variants in the HRAS oncogene have been described in agminated Spitz nevi, most of which were associated with an underlying nevus spilus. The use of targeted medical therapy for agminated Spitz nevi is not well understood. OBSERVATIONS: A girl aged 30 months presented with facial agminated Spitz nevi that recurred rapidly and extensively after surgery. Owing to the morbidity of further surgery, referral was made to a molecular tumor board. The patient’s archival nevus tissue was submitted for extended immunohistochemical analysis and genetic sequencing. Strong ROS1 protein expression was identified by immunohistochemistry. Consistent with this, analysis of whole-genome sequencing data revealed GOPC-ROS1 fusions. These results indicated likely benefit from the oral tyrosine kinase inhibitor crizotinib, which was administered at a dosage of 280 mg/m2 twice daily. An excellent response was observed in all lesions within 5 weeks, with complete flattening after 20 weeks. CONCLUSIONS AND RELEVANCE: Given the response following crizotinib treatment observed in this case, the kinase fusion was believed to be functionally consequential in the patient’s agminated Spitz nevi and likely the driver mutational event for growth of her nevi. The repurposing of crizotinib for GOPC-ROS1 Spitz nevi defines a new treatment option for these lesions, particularly in cases for which surgery is relatively contraindicated.

Predictive drug testing of patient-derived tumor organoids (PDTOs) holds promise for personalizing treatment of metastatic colorectal cancer (mCRC), but prospective data are limited to chemotherapy regimens with conflicting results. We describe a unified framework for PDTO-based predictive testing across standard-of-care chemotherapy and biologic and targeted therapy options. In an Australian community cohort, PDTO predictions based on treatment-naive patients (n = 56) and response rates from first-line mCRC clinical trials achieve 83% accuracy for forecasting responses in patients receiving palliative treatments (18 patients, 29 treatments). Similar assay accuracy is achieved in a prospective study of third-line or later mCRC treatment, AGITG FORECAST-1 (n = 30 patients). “Resistant” predictions are associated with inferior progression-free survival; misclassification rates are similar by regimen. Liver metastases are the optimal site for sampling, with testing achievable within 7 weeks for 68.8% cases. Our findings indicate that PDTO drug panel testing can provide predictive information for multifarious standard-of-care therapies for mCRC.