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Renal cell carcinoma (RCC) commonly presents with the triad of hematuria, flank pain, and a palpable abdominal mass, though all three together are uncommon. RCC arises from proximal tubular epithelium and can invade the renal vein, producing varicocele (especially left-sided). A classic paraneoplastic feature is ectopic secretion of parathyroid hormone–related peptide (PTHrP), causing hypercalcemia. Additionally, RCC may secrete erythropoietin (leading to polycythemia), renin (causing hypertension), or ACTH. Hypocalcemia is not typical; calcitonin-producing tumors are more characteristic of medullary thyroid carcinoma. Insulinomas cause hypoglycemia but are pancreatic in origin. Management depends on stage—partial or radical nephrectomy for localized disease, targeted therapy (tyrosine kinase inhibitors, immunotherapy) for advanced disease. Surveillance for paraneoplastic syndromes is essential during follow-up.