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Abstract

Chondromas are benign cartilaginous tumors which harbor mutations in IDH1 and IDH2 genes, which are also found in chondrosarcomas. These mutations, particularly the R132C and R172 variants, are common in central chondrosarcomas. Here we present a unique case of subungual chondroma with a novel PIK3CA mutations. While PIK3CA mutations are frequently found in various cancers, including breast, colorectal, and lung cancers, they are not a hallmark of chondromas. 

A 49-year-old female presented with a mass in the greater toe of 4 years duration first noticed as nail started to change shape after a painful pedicure but no other trauma. The pain and swelling waxed and waned over time. Excision was performed which revealed a benign cartilaginous mesenchymal neoplasm. The tumor was focally and weakly positive for S100 and negative for AE1/3, EMA, SOX10, p63 and SMA. The Ki-67 proliferative index was estimated at <1% by manual quantitation. Comprehensive genomic analysis demonstrated a hotspot activating PIK3CA mutations with no other pathogenic somatic variants or copy number alterations. No reportable gene fusion was detected by RNA fusion panel. Taken together, the overall features were that of a subungual soft tissue chondroma.

In summary, we describe a case of subungual chondroma with a previously unknown PIK3CA alteration. The biologic implication of the molecular genetic finding of activating PIK3CA gene mutation in chondroma is not known. In this regard, a prospective clinical surveillance would be prudent and merit consideration.