Recurrent clonal radiotherapy-associated fibroepithelial polyp of the pharynx: do low grade radiogenic stromal tumours exist? Case report.

There is a wide range of tissue changes that may arise after exposition to ionizing radiation. Most of these changes fall in the non-neoplastic category. Nevertheless, due to the damaging effect radiation has on the DNA, there is a risk of developing secondary tumours, usually high-grade sarcomas. Here, we present a case of an elderly man who developed recurrent fibroepithelial polyps of the pharyngeal mucosa. He had a history of ipsilateral squamous cell carcinoma of the tonsil 17 years before treated by complete surgical resection followed by adjuvant radiotherapy. Histologically, these polyps consisted of relatively well-defined, partially eroded mucosal projections with a fibro-myxoid and inflamed stroma lacking evident signs of malignancy. The 4th recurrence was submitted to DNA panel sequencing, which identified three pathogenic variants in the PTEN, DNMT3A, and TERT genes that were not present in the local normal tissue before radiotherapy. On further analysis, well-known and established radiation induced changes such as copy number (CN) alterations or a radiation signature were not detected. The clinical presentation and the mutations detected argue against a purely reactive, but rather a likely benign neoplastic process that is thought to have developed post-actinically, without clear evidence of malignancy (absence of atypia, no invasive growth, flat CN profile). This case report raises awareness of a possible association between radiotherapy and the subsequent development of a benign-appearing low-grade mucosal soft tissue neoplasm.