Two congenital cases of pigmented epithelioid melanocytoma with unique clinical and genetic features.

Pigmented epithelioid melanocytomas (PEM) are intermediate-grade melanocytic lesions with frequent lymph node involvement and rare metastases that tend to follow an indolent course with a favorable outcome. We report two unique cases of congenital PEM with PRKCA fusion transcripts: a multifocal PEM with an aggressive incompletely resectable scalp tumor and a solitary palmar PEM with newly reported ITGB5-PRKCA fusion. Through these case reports and a summary of previously reported cases, we outline the spectrum of disease of PEM and highlight the key clinical and histopathologic features associated with PEM with PRKCA fusion transcripts. We also discuss the treatment options and suggest that surgical excision without further adjuvant systemic treatment is reasonable first-line therapy given the favorable prognosis.

Late-onset tumors in rhabdoid tumor predisposition syndrome type-1 (RTPS1) and implications for surveillance.

Rhabdoid tumor predisposition syndrome type-1 (RTPS1) is characterized by germline pathogenic variants in SMARCB1 and development of INI1-deficient rhabdoid tumors in early childhood. Due to its poor prognosis, the risk of subsequent tumor development and the impact of surveillance at later ages are poorly understood. We retrospectively reviewed individuals referred to the Cancer Genetics Program at The Hospital for Sick Children for SMARCB1 genetic testing and/or surveillance for RTPS1. In addition, to explore characteristics of late-onset tumors in RTPS1, a literature review was conducted. Of eighty-three individuals (55 probands and 28 family members), 12 probands and 4 family members were genetically confirmed with RTPS1. Four pediatric probands with RTPS1 underwent surveillance. An additional three individuals, including one patient with 22q11.2 distal deletion without history of tumor, one patient with negative genetic testing results but clinically diagnosed with RTPS1, and one sibling identified through cascade testing, underwent surveillance. Three patients with RTPS1 developed tumors between the ages of 9 and 17, including malignant rhabdoid tumors (N = 3), schwannomas (N = 4), and epithelioid malignant peripheral nerve sheath tumor (N = 1). Three of these lesions were asymptomatically detected by surveillance. A literature review revealed 17 individuals with RTPS1 who developed INI1-deficient tumors after age five. Individuals with RTPS1 remain at elevated risk for developing INI1-deficient tumors after the peak age of rhabdoid tumor in early childhood. Extension of surveillance beyond 5 years of age could lead to improved survival and reduced morbidity for these patients, and prospective evaluation of revised approaches will be important.