The majority of type 2 PRCC has high Fuhrman grade nuclei with prominent nucleoli. Signs and Symptoms
Due to its asymptomatic nature, PRCC is often undetectable, and the majority of cases are incidentally diagnosed during the radiological workup of unrelated diseases. Its clinical manifestations are similar to those of clear cell RCC, which are the classical triad of renal cell carcinoma (hematuria, flank pain and palpable abdominal mass; only 6-10% of patients) or even nonspecific symptoms including fatigue, weight loss, fever, and anorexia. Since early diagnosis is relatively uncommon, PRCC patients may experience symptoms caused by the metastatic spread to secondary sites. Specifically, metastasis occurs most frequently in the lungs followed by bone and the brain, exhibiting a wide range of symptoms including bone pain to a persistent cough. Causes
Currently, the exact cause of PRCC remains unclear. Possible risk factors have been identified that contribute to PRCC development, which include genetic mutations, hereditary syndrome, renal injuries, and lifestyle factors. Germline mutation of c-MET oncogene and fumarate hydratase gene elevates the risk of type 1 and type 2 PRCC respectively through distinct signaling pathways. Regarding hereditary conditions, patients with hereditary papillary renal cancer syndrome showed a greater risk of type 1 PRCC, whereas those with hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome have an increased risk of type 2 PRCC. Moreover, patients who experienced chronic kidney diseases or acute kidney injury exhibited a higher incidence of PRCC. Additionally, other risk factors such as smoking, obesity, and high blood pressure can influence the pathogenesis of PRCC.
Pathogenesis
Different molecular mechanisms are involved in PRCC development, which further result in distinct histologic features and clinical outcomes.Type 1 PRCC is caused by a genetic mutation or a gain in chromosome 7 where the MET gene is positioned, resulting in the promotion of oncogenic pathways in renal epithelial cells. Typically, the MET gene is upregulated for renal tissue repair and regeneration by encoding the receptor tyrosine kinase c-MET of hepatocyte growth factor. However, activation of the oncogenic pathway in the MET gene will manifest invasion, anti-apoptosis, angiogenesis, and metastasis.Type 2 PRCC is associated with irregularity of several signaling pathways, which includes CDKN2A silencing, mutation in chromatin-modifying genes, and a GpG island methylator phenotype (CIMP). CDKN2A is a tumor suppressor gene, while loss of its expression results in enhanced tumorigenesis and metastasis. Moreover, mutation of gene involved in chromatin remodeling (SETD2, BAP1, or PBRM) may lead to higher rate of TFE3/TFEB fusion. Additionally, CIMP papillary renal cell carcinoma tumors exhibited somatic FH gene mutation, which is closely associated with HLRCC syndrome. Diagnosis
Currently, cross-sectional imaging with computed tomography (CT) and magnetic resonance imaging (MRI) is known as the best option for diagnosing papillary renal tumors. Computed tomography (CT)
Contrast-enhanced computed tomography (CT) is most commonly used to identify the subtypes of RCC. PRCC can be differentiated from other types of RCC due to its distinguishing features, displaying a small hypovascular renal tumor on T2 weighted images.