Clear cell ‘sugar’ tumour of the lung

Abstract

© BMJ Publishing Group Limited 2021. No commercial reuse. See rights and permissions. Published by BMJ. DESCRIPTION A 43yearold woman was referred to our thoracic surgery department following multidisciplinary team (MDT) discussion for a concerning 7×5 mm pulmonary nodule in the medial right upper lobe which was discovered incidentally on a CT thorax abdomen pelvis (figure 1) as part of surveillance for her previous cervical cancer. This woman has a history of squamous cell carcinoma of the cervix (stage IIB), which was diagnosed in 2012 and managed with chemoradiotherapy. Unfortunately, she had a number of complications secondary to radiotherapy including a colovesical fistula (2013), defunctioning loop ileostomy formation (2014), vesicovaginal fistula (2014) and recurrent urirnary tract infection (UTIs). In late 2014, she developed a 4 cm cutaneous squamous cell metastasis in her right flank which was surgically excised. Her other medical history includes lupus and hypothyroidism. She is a nonsmoker. Following identification of the pulmonary nodule on CT TAP, she underwent PET CT. However, the subcentimetre nodule was too small to resolve with PET and remained indeterminant. No other concerning areas of uptake were identified. The differential diagnosis clinically was metastatic cervical carcinoma or a primary lung neoplasm. She subsequently underwent right videoassisted thoracoscopic surgery upper lobe wedge resection. Macroscopic examination of the lung wedge revealed a circumscribed, firm, white nodule, measuring 7 mm in largest dimension, excised by 1 mm to the closest resection margin. Microscopic examination revealed the nodule to be a wellcircumscribed tumour composed of nests of bland cells with clear and granular cytoplasm, set in a hyalinised stroma (figure 2). Significant cytological atypia was not seen. Mitoses were not evident. Immunohistochemistry showed that the lesional cells stained positively for HMB45, with focal positivity for melan A. The cytoplasmic granules stained positively with periodic acid–Schiff and negatively with periodic acid–Schiff diastase, confirming the presence of glycogen. Immunohistochemistry for SOX10, S100, desmin, synaptophysin, PAX8, ERG, oestrogen receptor, AE1/3, p63, CK5/6, TTF-1 and napsin A were negative. Features of metastatic squamous cell carcinoma were not seen. Following histopathological analysis (figure 2), the diagnosis of clear cell ‘sugar’ tumour (CCST) of the lung was made that showed no malignant features. As this was a benign pulmonary lesion, this woman’s followup will be guided by her primary cervical cancer. CCST has been recently recognised to belong to the perivascular epithelioid cell tumour (PEComa) family of tumours. These are rare mesenchymal neoplasms that appear to arise from perivascular epithelioid cells and have morphological, immunophenotypic and ultrastructural similarities. PEComas usually have a combined myogenic and melanocytic immunophenotype. They occur more commonly in women. PEComas include specific entities such as CCST of the lung, angiomyolipoma and pulmonary lymphangioleiomyomatosis, and can occur as PEComas in the viscera, soft tissue and skin. Most PEComas are sporadic, but an association with tuberous sclerosis complex has been shown in angiomyolipoma, lymphangioleiomyomatosis and very rarely CCST. CCST is a rare tumour arising in the lung. It was first described by Liebow and Castleman. CCST usually arise in the periphery of the lung, are often incidentally detected, and can measure up to 7 cm in size. They are composed of nests of uniform cells that have both clear and granular cytoplasm, welldefined cell borders Figure 1 CT thorax abdomen pelvis—new 7x5 mm nodule in medial right upper lobe. Figure 2 (A) nests of bland cells with clear and granular cytoplasm within a hyalinised stroma, H&E stain ×100 magnification, (B) H&E stain x400 magnification, (C) positive cytoplasmic periodic acid– Schiff staining of glycogen within tumour cells, x400 magnification, (D) tumour cells showing positive HMB45 immunohistochemistry, x400 magnification.