Papillary renal cell carcinoma — type 1, type 2 and what the label means

Papillary renal cell carcinoma is the second commonest subtype of renal cell carcinoma, after clear cell. It takes its name from the way the tumour cells grow: along thin, finger-like fronds called papillae, which a pathologist sees once the tissue is examined under a microscope. It begins in the lining of the tiny filtering tubes of the kidney, the same place other renal cell carcinomas start. Many are found by chance, on a scan requested for something else entirely. Papillary tumours are also more likely than other subtypes to appear in more than one place in the same kidney, which is why both kidneys are reviewed carefully on imaging before any plan is made.

Type 1 and type 2 were descriptions of how the cells look, not two different organs or two different stages. In type 1 the papillae are lined by a single layer of small cells with pale cytoplasm, and these tumours are usually lower grade and slower moving. Type 2 cells are larger, with more strongly staining cytoplasm and more prominent nucleoli, and tumours labelled that way behaved less predictably. The important point is that type 2 was never one disease. It was a mixed group, and several tumours once filed under it are now recognised as separate entities with their own biology.

Neither subtype is automatically better or worse, and the honest answer is that stage and grade tell you far more than the label does. Papillary tumours are often found while still confined to the kidney, and low grade type 1 tumours in particular can be slow and undemanding. Tumours in the group once called type 2 can behave more aggressively. What the subtype really changes is the plan rather than the seriousness: papillary renal cell carcinoma does not respond to systemic treatment in the same way clear cell does, so the drug classes considered for advanced disease are not identical. Stage, grade and subtype are always read together.

Because the classification changed. Pathologists found that the type 2 category was not a single disease but a collection of different tumours that happened to share an appearance, and that two pathologists did not always assign the same type to the same slide. The current World Health Organization classification therefore reports papillary renal cell carcinoma as one entity, describes the grade and any unusual features separately, and treats the distinct tumours once filed under type 2 as diagnoses in their own right. Many reports still carry the old type, and that is not an error. Ask your oncologist to read the description alongside it.

It depends on the stage. For a tumour still confined to the kidney, removing it is usually the main treatment: CION coordinates partial, radical and robotic nephrectomy, and ablation where that suits better, with specialist urology, uro-oncology and interventional radiology partners, where these may also be billed. Very small tumours are sometimes watched instead, with the imaging monitoring run in-house. For advanced disease the treatment is systemic and medical-oncology led at CION, using targeted TKI classes, mTOR inhibition and immunotherapy along NCCN lines. Because the evidence base is smaller than for clear cell, clinical trial options are worth asking about. Chemotherapy is not effective against renal cell carcinoma.

It can, although most cases are not inherited. There is a hereditary form of papillary kidney cancer, driven by a change in the MET gene, in which tumours tend to appear in both kidneys and at more than one site, often at a younger age than usual. A separate inherited condition involving the fumarate hydratase gene causes skin and uterine growths alongside a kidney cancer that used to be grouped under type 2. The signals worth raising are tumours in both kidneys, several tumours in one kidney, a young age at diagnosis, or a close relative with kidney cancer. Genetic counselling is available in-house at CION.