Beyond the Usual: Breast, Pituitary and Gastric Metastases from Clear Cell Renal Cell Carcinomas—A Case Series with Review of Literature

Background and Clinical Significance: Clear cell renal cell carcinoma (ccRCC) is notorious for its aggressiveness and great propensity to metastasize to virtually any organ, with a dismal five-year survival rate. While metastases from ccRCC typically occur in the lungs, lymph nodes, bones and liver, involvement of atypical locations such as the breast, pituitary gland and stomach is extremely rare. These unusual metastases can masquerade as primary tumours at their respective sites, posing significant diagnostic challenges. Case Presentation: Here, we describe three cases of metastatic ccRCC to unusual anatomical sites following nephrectomy: (1) a patient who presented with a suspicious left-sided breast mass and synchronous liver and lung metastases six months following the initial diagnosis of ccRCC; (2) a patient who presented with diplopia, found to have a pituitary lesion four months after nephrectomy; and (3) a patient with known pre-existing lung metastases who developed upper gastrointestinal bleeding one year post-nephrectomy, in whom oesophagogastroduodenoscopy (OGDS) revealed an 8 mm pedunculated gastric polyp. Histopathological examination following biopsies of these lesions showed compact nests and sheets of malignant cells with clear to eosinophilic cytoplasm and distinct membranes. Immunohistochemically, these malignant cells demonstrated CD10 immunopositivity, and were negative for CK7 and CK20, in keeping with the diagnosis of metastatic ccRCC. Conclusions: This case series illustrates the rare metastatic behaviour of ccRCC with its potential to spread to uncommon sites. Awareness of such presentations is crucial, particularly in patients with a known history of ccRCC, as these lesions may clinically and radiologically mimic primary tumours of the affected sites. Careful evaluation of its histomorphological features and judicious use of immunohistochemical panels, together with clinical and radiological correlations, is the key to arriving at an accurate diagnosis.