Two Cases of STAT6-Positive, Primary Conjunctival Giant Cell-Rich Solitary Fibrous Tumour (Giant Cell Angiofibroma) with Some Unusual Histological Features.

An 84-year-old male presented with a history of a slowly growing lesion beneath the right lower lid. Examination showed a right-sided mass in the inferior bulbar conjunctiva, measuring approximately 10 × 6 mm. The lesion was excised and showed a giant cell-rich solitary fibrous tumour (GCR-SFT) with pseudo-vascular spaces with benign cytology, with STAT6, expressed in the spindle, ovoid, and tumour giant cells. A second case, a 26-year-old white female, presented with a 12-month history of a gradually expanding lesion in left inferior bulbar conjunctiva. Examination showed a well-defined, dome-shaped pink fleshy mass of 10 × 7 × 2 mm, on the inferior bulbar conjunctiva and abutting the inferior fornix. Excision followed by histology showed a similar appearance to the first case except that the multinucleate giant cells closely resembled Touton giant cells and did not show the rather hyperchromatic crowded nuclei of the giant cells observed in the first case. No pseudo-vascular spaces were identified. The tumour cells, including the Touton-like multinucleate giant cells, displayed nuclear positivity for STAT6. An unexpected feature was the presence of a Melan A- and Sox10-positive population amongst the GCR-SFT, postulated to be a subepithelial melanocytic nevus colliding with the GCR-SFT.