Unusual appearance of perirenal fibrosis in renal cell carcinoma simulating a tumour.

Desmoplastic reaction of the stroma is a part and parcel of several malignancies. It may be seen within or at a site distant from the main tumour. Irrespective of the site of fibrosis in tumours, it portends a poor prognosis as it is generally associated with invasion and metastasis. In this report, we present a unique case of a 78-year-old male patient with clear cell renal carcinoma (CCRC) who presented with a lump in the right loin. On magnetic resonance imaging scan, the mass was arising from the middle part of the right kidney. The nephrectomy was done and specimen on examination revealed a variegated tumour with another whitish solid mass in the surrounding perirenal fat. The kidney tumour showed features of CCRC, whereas whitish mass was entirely composed of proliferating spindle cells. Therefore, the mass mimicked a second tumour not only on gross but even on microscopy. The special stains (Elastic-van Gieson, Masson-Trichrome, Periodic acid schiff's, alcian blue and mucicarmine), immunostaining (cytokeratin, vimentin, epithelial membrane antigen, smooth muscle actin, S-100, HMB-45, CD34 and CD117) patterns and ultrastructural features all, however, favoured it to be an extensive peritumoural fibrotic reaction rather than a neoplasm. The observation provokes important questions like whether the reaction in the index case is an example of tumour-induced fibrosis or is an unassociated phenomenon and, in the case of former, what are factors that govern the extent and site of fibrosis, i.e. intratumoural, peritumoural or away from the tumour. The finding may also help in further research and understanding of the role of stroma in cancer progression and developing stromal antigen-targeted therapies in CCRC.