Extrapleural solitary fibrous tumours (SFTs) are rare tumours characterized by patternless spindle cells with haemangiopericytoma-like vascular spaces. Previously the tumours have been classified as haemangiopericytoma, an entity that is now considered obsolete. We report a case of extrapleural SFT arising in the soft tissue of the chest wall. The patient was a 31-year-old Malay lady presenting with a mobile swelling of the right chest wall for more than five years. During excision the tumour was noted to be well-circumscribed and yellowish in colour, giving an impression of lipoma. Microscopically, the tumour had patternless architecture, characterized by hypocellular and hypercellular areas. It was composed of uniform, spindle-shaped cells displaying oval nuclei, inconspicuous nucleoli, pale cytoplasm and indistinct cell borders. The mitotic count was 2 per 10 HPF. Branching, medium-sized thin-walled blood vessels in a haemangiopericytomatous growth pattern, some with hyalinised wall were identified. The neoplastic cells were immunoreactive to CD99 and CD34 and were non-immunoreactive to Desmin, Smooth Muscle Actin, S100 protein and EMA. We elucidate the challenges in diagnosing this tumour in this unusual location.
Soft tissue tumours are a group of remarkably diverse neoplasms that frequently pose significant diagnostic challenges to general pathologists. This study aimed to compare the agreement of histopathological diagnoses between general pathologists from various referral institutes and the referred soft tissue pathologist in a tertiary centre. The common discrepancies and their causes are also presented here. A retrospective study was conducted on 243 cases of potential soft tissue tumours referred to Hospital Kuala Lumpur, Malaysia over a period of 5 years. Reports by the referring pathologists and the soft tissue pathologist were compared based on tumour classification and tumour behaviour. Overall, there was moderate agreement in soft tissue tumour diagnoses in both tumour classification (weighted κ = 0.423) and tumour behavior (weighted κ = 0.548). The highest agreement of tumour classification was seen in the adipocytic tumours (21/28 cases), Ewing sarcoma (5/7 cases) and smooth-muscle tumours (3/5 cases). The highest rates of discrepancies were the so-called fibrohistiocytic tumours (7/11 cases), vascular tumours (9/15 cases) and undifferentiated/ unclassified sarcomas (19/32 cases). Full agreement for tumour behaviour was seen in 178 cases and there were 21 cases of zero agreement. Liposarcoma, alveolar soft part sarcoma and benign fibrous histiocytoma were the most frequent benign/malignant diagnostic discrepancies. The most common causes of discrepancy were wrong morphological interpretation followed by insufficient immunohistochemical stains performed. In conclusion, review of diagnosis by a pathologist specialized in soft tissue improves the quality of diagnosis in these heterogenous and rare tumours. A good panel of immunohistochemical stains with additional molecular study is crucial in the general hospital laboratories practice.