Familial wild-type gastrointestinal stromal tumour in association with germline truncating variants in both SDHA and PALB2

Abstract

Gastrointestinal stromal tumour (GIST) is a mesenchymal neoplasm arising in the gastrointestinal tract. A rare subset of GISTs are classified as wild-type GIST (wtGIST) and these are frequently associated with germline variants that affect the function of cancer predisposition genes such as the succinate dehydrogenase subunit genes (SDHA, SDHB, SDHC, SDHD) or NF1. However, despite this high heritability, familial clustering of wtGIST is extremely rare. Here, we report a mother-son diad who developed wtGIST at age 66 and 34 years, respectively. Comprehensive genetic testing revealed germline truncating variants in both SDHA (c.1534C>T (p.Arg512*)) and PALB2 (c.3113G>A (p.Trp1038*)) in both affected individuals. The mother also developed breast ductal carcinoma in-situ at age 70 years. Immunohistochemistry and molecular analysis of the wtGISTs revealed loss of SDHB expression and loss of the wild-type SDHA allele in tumour material. No allele loss was detected at PALB2 suggesting that wtGIST tumourigenesis was principally driven by succinate dehydrogenase deficiency. However, we speculate that the presence of multilocus inherited neoplasia alleles syndrome (MINAS) in this family might have contributed to the highly unusual occurrence of familial wtGIST. Systematic reporting of tumour risks and phenotypes in individuals with MINAS will facilitate the clinical interpretation of the significance of this diagnosis, which is becoming more frequent as strategies for genetic testing for hereditary cancer becomes more comprehensive.

Fig. 1. Histology and SDHB immunohistochemistry on GIST samples from SDHA/PALB2 diad.

A, C Haematoxylin and eosin staining on samples from son and mother, respectively. B, D Loss of SDHB immunostaining on samples from son and mother, respectively. Non neoplastic cells show a retained mitochondrial staining pattern which can be appreciated in B and D.

Fig. 2. Integrative genomics viewer screenshot from coordinate of SDHA variant.

BAM files resulting from sequencing DNA extracted from tumour. Loss of SDHA wild-type allele shown in samples from both members of diad as indicated by predominance of variant (denoted by red colour) bases.

Fig. 3. Sanger sequencing chromatograms from coordinate of PALB2 variant resulting from sequencing DNA extracted from tumour.

Retention of wild-type allele indicated by dual peak at site of variant.