Sarcomatoid Variant of Renal Cell Carcinoma and a Comprehensive Exploration of Its Molecular Pathogenesis

Renal cell carcinoma (RCC) is a common neoplasm of the kidney.A rare, highly aggressive form of RCC that can arise in any subtype of this disease is the sarcomatoid type.RCC with sarcomatoid differentiation (sRCC) has a high likelihood of metastasising and, thus, shows a poor prognosis.Signs and symptoms are mostly non-specific.Here, we report a case of a 56-year man who was misdiagnosed as a pyonephrotic kidney based on imaging and was found to have sRCC on histopathological examination.He presented to the emergency department with a complaint of long-standing left flank pain with no other associated symptoms.An ultrasound kidney, ureter, and bladder (KUB) revealed moderate hydronephrosis with thick internal echoes in the left kidney.A subscapular collection measuring 150 ml was also found.An ultrasound-guided pigtail catheter was then placed and around 300 ml of haemorrhagic fluid with necrotic tissue was aspirated.CT KUB showed a left grossly hydronephrotic kidney, measuring 13.5 5.3 cm, with a thinned-out cortex.A provisional diagnosis of the left pyonephrotic kidney was made, and a left nephrectomy was performed.On histopathological examination, it was diagnosed as sRCC.On a follow-up visit after one month, CT-chest abdomen, and pelvis (CAP) was performed, which revealed metastatic disease involving the lungs.This case report serves to highlight that the diagnosis of malignancy should be considered in patients who present with hydronephrotic obstructed kidneys with clots.Contrast studies and ultrasound-guided biopsy can help in preoperative diagnosis.sRCC has a rapid progression, and strict monitoring is recommended.