Collecting duct RCC and renal medullary carcinoma — rare, fast-moving, and treated differently

Collecting duct carcinoma, sometimes still called Bellini duct carcinoma, is a rare kidney cancer that begins in the collecting ducts deep in the medulla, the inner part of the kidney where urine is concentrated. Most kidney cancers start in the outer cortex instead, which is one reason this one looks and behaves differently. On a scan it often grows in an infiltrating way through the kidney rather than sitting as a neat round lump, and it is more often found once it has already spread beyond the kidney. The diagnosis is made on tissue, and pathologists reach it partly by excluding other cancers that can look very similar, especially urothelial cancer of the renal pelvis.

Renal medullary carcinoma is seen almost only in people who carry sickle cell trait, and less often in those with sickle cell disease. The usual explanation is that the low-oxygen, high-salt environment of the renal medulla makes red cells carrying haemoglobin S sickle in that exact spot, and the repeated injury that follows sets the stage for the cancer. It typically appears in young people, more often male, and more often in the right kidney. Carrying the trait does not mean you will develop it, because the great majority of carriers never do. But in a young person with sickle cell trait and blood in the urine or flank pain, it is a possibility a doctor should actively rule out rather than assume away.

They begin in a different part of the nephron, they look different under the microscope, and they are driven by different biology. Clear cell renal cell carcinoma arises in the proximal tubule and is usually linked to the VHL pathway. Collecting duct and medullary carcinoma arise from the distal nephron, and medullary carcinoma is defined by loss of the SMARCB1 protein in the tumour cells. That difference is not academic. The systemic treatments that work best in clear cell disease, meaning VEGF-targeted therapy and immune checkpoint blockade, cannot be assumed to behave the same way here. NCCN groups both under non-clear-cell kidney cancer and asks for a subtype-specific plan rather than a default one.

It starts with imaging, usually a contrast CT of the abdomen and sometimes an MRI, where both tend to show a centrally placed, infiltrative mass rather than a well-defined tumour. Because that appearance overlaps with urothelial cancer of the renal pelvis and with severe infection, tissue is needed to be sure. A core biopsy, or the specimen after surgery, is examined with immunohistochemistry: loss of SMARCB1 staining, also written as INI1, is the defining feature of renal medullary carcinoma, while collecting duct carcinoma remains largely a diagnosis of exclusion. At CION the CT, MRI, biopsy and blood work, including haemoglobin studies where sickle cell trait is suspected, are delivered in-house. PET-CT, where it is needed, is coordinated with specialist partner centres.

Yes, and that is the main reason the exact subtype on your report matters. Where the tumour is localised and operable, surgery is the anchor of treatment. At CION that surgery is coordinated with specialist urology and uro-oncology partners, where it may also be billed, rather than being carried out in-house. For advanced disease the approach used in clear cell kidney cancer is not simply transferred across: platinum-based cytotoxic chemotherapy has an established role in medullary carcinoma, and choices in collecting duct carcinoma are made case by case. NCCN encourages clinical trial participation in both. Systemic treatment and radiation are delivered in-house by our medical oncology team, and the routes are set out on our kidney cancer treatment page.

It is a reasonable thing to ask for, and no treating doctor should read it as distrust. Both diagnoses are uncommon, both are reached partly by excluding look-alikes, and both change the treatment plan considerably, so a specialist re-read of the slides with the right immunohistochemistry performed is worth having before anything is settled. It also matters that the plan is made by a team rather than by one person. Every case at CION goes to a tumour board, the first consultation and the written second opinion are free, and there is no commitment to start treatment with us. Bring the pathology report and the scan discs you already have.