Molecular Characterization of Multifocal Granular Cell Tumors

Melan-A-Positive Granular Cell Tumor With Extensive Intraneural and Perineural Spread: A Rare Case Report

Cutaneous granular cell tumors (GCTs) are rare tumors that typically exhibit benign clinical behavior and are likely of Schwann cell origin. Some histologic and immunohistochemical variants of GCTs may present challenges due to infiltrative growth patterns, perineural invasion, and expression of Melan-A. In this case report, we present a 27-year-old male who had previously been diagnosed with a typical GCT on the back a few years ago. The current biopsy from the proximal palm demonstrated a cytologically similar tumor with extensive perineural spread and notable positivity for Melan-A. Although uncommon, these features are consistent with the histological appearances of GCTs. The current views on the histogenesis of GCTs, clinical associations, differential diagnosis with melanoma, and histological criteria for malignant GCTs are discussed. A panel of immunohistochemical stains, including Inhibin-α and preferentially expressed antigen in melanoma (PRAME), is proposed for use in rare instances of Melan-A-positive GCTs.

Utility of sequencing for ATP6AP1 and ATP6AP2 to distinguish between atypical granular cell tumor with junctional component and melanoma

BACKGROUND

Granular cell tumor (GCT) is a S100+ neoplasm with atypical and malignant variants. Similar to melanocytic neoplasms, the tumors make nests and can have junctional components raising a differential diagnosis of melanoma. Nevi and melanomas may also have granular cell cytoplasm. MelanA is useful in distinguishing melanocytic from granular cell lineage, but increasingly MelanA/SOX10 negative melanomas have been recognized by correlation with molecular methods.

METHODS

We encountered several cases with morphologic overlap between melanoma and atypical GCT necessitating additional molecular workup. We sequenced two cases and searched our archive for similar cases of GCT with overlapping features of melanocytic lineage.

RESULTS

In our two index cases, we excluded melanoma driver mutations and identified frameshift or premature stop codons in ATP6AP1/2 pathognomonic of granular cell lineage. Data retrieved from Cosmic identified 24 melanomas with missense single nucleotide variants (SNVs) in ATP6AP1 but no frameshift or premature stop codons. Twenty-one melanomas had missense SNVs in ATP6AP2. One melanoma had a premature stop codon in ATP6AP2, but this lesion also had a melanoma-associated driver mutation NRASQ61K. We found 1 of 23 additional cases of GCT in our archives with a junctional component and no additional cases with maturation.

CONCLUSIONS

Atypical and malignant GCT can have histopathologic overlap with melanoma. Frameshift and premature stop codons in ATP6AP1/2 are specific for granular cell lineage, and capable of excluding melanoma, in the absence of known melanoma-associated driver mutations.

Mesenchymal Tumors of the Breast: Fibroblastic/Myofibroblastic Lesions and Other Lesions

Mesenchymal breast tumors are a rare and diverse group of tumors that present some of the most challenging cases for multidisciplinary breast cancer teams. As a result of overlapping morphologies and a lack of large-scale studies on these tumors, practices are often heterogeneous and slow to evolve. Herein, we present a non-systematic review that focuses on progress, or lack thereof, in the field of mesenchymal breast tumors. We focus on tumors originating from fibroblastic/myofibroblastic cells and tumors originating from less common cellular origins (smooth muscle, neural tissue, adipose tissue, vascular tissue, etc.).

A Rare Case of Multifocal Asynchronous Benign Granular Cell Tumors with PIK3CA Subclonal Mutation Identified in One Tumor by Next-Generation Sequencing

Granular cell tumor (GCT) is a benign neuroectodermal tumor typically in the dermis or subcutis, although deep soft tissues and organs are occasionally involved. Multifocal GCTs are estimated to occur as many as 10% of patients. A 40-year-old female presented with multiple GCTs asynchronously involving various body sites including gastrointestinal, gynecologic, breast, urinary, and soft tissue systems. Pathologic examinations suggested benign GCTs. TruSight Tumor 170 next-generation sequencing (NGS) analysis performed on four resected tumors revealed subclonal mutation of PIK3CA p.H1047R identified in the esophageal GCT but not in the right vulva or the two cecal GCTs, suggesting that each is a primary tumor with a distinct genetic profile, rather than metastasis. PIK3CA p.H1047R is a common mutation in many cancers. Our benign GCT case demonstrates PIK3CA mutation with a low mutant allele frequency of 7%, which may represent an evolving subclone and might confer a more aggressive behavior.