Page 65 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

Malignant transformation of pleomorphic adenoma: Proof of principle
A year later, a lump medial to the sternocleidomastoid muscle was biopsied because the patient refused FNA, and this lesion was classified as suspect for adenocarcinoma. A modified radical neck dissection was performed (levels 1-5) with reconstruction of the accessory nerve and the wound defect. Pathology showed a multinodular basal cell adenocarcinoma (Figure 1C, F), reaching into the resection surface. All 24 lymph nodes were free of tumor. Postoperative RT to the neck (60 Gray) was administered.
In order to understand the clinical behaviour, all previous slides were reviewed and molecular analysis was performed. DNA and RNA from all three lesions and normal tissue was isolated. Targeted next generation sequencing (NGS) was performed on an Ion Torrent S5XL prime system using a custom-made panel for mutation and copy number variation detection using single nucleotide polymorphisms (SNPs) on 12 chromosomes (panel information supplementary material, Table S1)[22,23]. In addition, RNA-based gene fusion detection using the Archer FusionPlex Sarcoma panel (ArcherDx, Boulder, CO, USA) was performed. Immunohistochemistry for Ki-67 and p53 was performed. The medical ethical committee of the Erasmus Medial Center Rotterdam, the Netherlands approved this study (MEC-2020-0270).
Results
All three lesions showed the same LIFR/PLAG1 gene fusion (supplementary material, Figure S1), an identical somatic frameshift mutation in the PIK3R1 gene (supplementary material, Figure S2) and identical patterns of allelic imbalance on chromosomes 5, 7 and 8 (Figure 4 and supplementary material, Figure S3), confirming their clonal relation.
Additionally, the first recurrent tumor showed a TP53 p.R248Q (c.743G>A) mutation with a variant allele frequency (VAF) of 46% (supplementary material, Figure S2). The second recurrent tumor showed a different TP53 mutation: TP53 p.Y220C (c.659A>G) with a VAF of 51% (supplementary material, Figure S2).
The low-level/subclonal presence of both TP53 mutations found in the two recurrences was investigated in the three tumor samples with a very sensitive NGS approach using unique molecular identifiers (ThermoFisher OncomineTM Lung
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