Tubulocystic Renal Cell Carcinoma: Understanding Your Pathology Report

Section Editor: Trevor Flood MD FRCPC
July 18, 2026

Tubulocystic renal cell carcinoma is a rare type of kidney cancer. It starts with the cells that line the tiny tubes inside the kidney, called nephrons, which filter the blood and produce urine. The name describes what the tumor looks like: it is built from small tubes and larger fluid-filled sacs called cysts, which give it a spongy, bubble-like appearance. It makes up fewer than 1 in 100 kidney cancers and is found most often in men in their fifties and sixties.

The most important thing to know about this diagnosis is reassuring. In its pure form, tubulocystic renal cell carcinoma grows slowly and is cured by surgery in almost every case. Spread to other parts of the body is rare. Your pathology report matters here less for predicting danger and more for confirming that the tumor is the pure type, because a small number of tumors that look tubulocystic turn out on closer testing to be a different and more concerning kidney cancer, as explained below.

This article will help you understand the findings in your pathology report for tubulocystic renal cell carcinoma, what each term means, and why it matters for your care.

What causes tubulocystic renal cell carcinoma?

The cause of tubulocystic renal cell carcinoma, a rare kidney cancer, is not known. Almost all of these tumors happen by chance, with no event or exposure that explains why they developed, and there is no established link to smoking, obesity, or any inherited condition. When researchers have examined the genes of these tumors, they have found relatively few changes, most often a gain of chromosome 17 and loss of chromosomes 9 and Y. These findings help confirm that tubulocystic renal cell carcinoma is its own distinct kidney cancer rather than a version of another type, but they are not used to guide treatment.

For many years this tumor was thought to be closely related to papillary renal cell carcinoma, partly because the two are sometimes found together in the same kidney. Genetic studies have since shown that pure tubulocystic renal cell carcinoma is a separate disease. When a tumor shows a mix of tubulocystic and papillary growth, pathologists no longer call it tubulocystic renal cell carcinoma at all, a point that matters for how these tumors are named and is explained in the diagnosis section below.

What are the symptoms of tubulocystic renal cell carcinoma?

Most people with tubulocystic renal cell carcinoma, a rare kidney cancer, have no symptoms. These tumors are usually found by accident during an ultrasound, CT scan, or MRI performed for an unrelated reason. When symptoms do occur, they may include:

Blood in the urine, which can make the urine look red, pink, or brown.
Pain or a dull ache in the back or the side of the abdomen.
A lump or fullness in the abdomen or side.

Many of these symptoms are caused far more often by conditions other than cancer, which is why tests are needed to make the diagnosis. Spread of this tumor to another part of the body (a process called metastasis) is rare.

How is the diagnosis made?

The diagnosis of tubulocystic renal cell carcinoma is made when a pathologist examines kidney tissue under a microscope. The tumor is usually first seen as a mass with many small cysts on an ultrasound, CT scan, or MRI. For most kidney masses, the next step is surgery to remove the tumor rather than a needle biopsy, and this tumor in particular is hard to recognize on a small biopsy sample, because the features that define it are spread across the whole tumor.

Under the microscope, tubulocystic renal cell carcinoma has an appearance distinctive enough that pathologists often recognize it at a glance. It is made entirely of small tubes and larger cysts, separated by bands of dense, scar-like supporting tissue called stroma. The tubes and cysts are lined by a single layer of cells that are flattened, cube-shaped, or hobnail-shaped, meaning the rounded top of the cell bulges into the space like the head of a nail. The cells have abundant pink cytoplasm and, notably, large nucleoli (prominent round structures inside the nucleus). These large nucleoli would count as high grade in other kidney cancers, but in tubulocystic renal cell carcinoma they are simply part of the normal appearance of the tumor and are not a sign that it will behave badly. This point is explained further in the grading section below.

Two rules define the pure form, and both matter for your diagnosis. First, the tumor must be made only of tubes and cysts. If a pathologist finds areas of solid growth, papillae (finger-like projections), or sarcomatoid cells mixed in, the tumor is not classified as pure tubulocystic renal cell carcinoma and is instead classified by the features those other areas show. Second, and most important, a tumor called fumarate hydratase-deficient renal cell carcinoma can closely mimic this appearance while behaving very differently, so distinguishing the two is the pathologist’s central task. A test called immunohistochemistry, which uses special stains to detect proteins inside cells, is used to distinguish them. Tubulocystic renal cell carcinoma is positive for PAX8 (which confirms the tumor started in the kidney), positive for AMACR, and, crucially, keeps its fumarate hydratase (FH) protein, whereas fumarate hydratase-deficient renal cell carcinoma loses it. A retained FH stain and a negative 2SC stain confirm the pure tubulocystic diagnosis and its favorable outlook. Once the diagnosis is confirmed, imaging of the chest and abdomen is used to check for spread.

Histologic grade

Most kidney cancers are given a grade, a number from 1 to 4 describing how abnormal the cells look, using the WHO/ISUP system based on how easily the nucleoli can be seen under the microscope. Tubulocystic renal cell carcinoma is a special case, and understanding why prevents a common misreading of the report.

According to the grading system, the large nucleoli in this tumor correspond to grade 3, and some reports state this. But the grade means something different here than it does in other kidney cancers. In clear cell renal cell carcinoma, grade 3 nucleoli mark a tumor more likely to spread. In tubulocystic renal cell carcinoma, those same nucleoli are present in essentially every case, including the many tumors that are completely cured by surgery. The prominent nucleoli are a built-in feature of the tumor, not a warning sign. For this reason, the WHO/ISUP grade is not used to predict behavior in tubulocystic renal cell carcinoma the way it is in clear cell and papillary renal cell carcinoma, and a grade 3 label on your report does not carry the meaning it would for those cancers. What predicts behavior here is whether the tumor is pure, which is covered in the diagnosis and prognosis sections.

Tumor size

Your pathology report will state the size of the tubulocystic renal cell carcinoma, measured in centimeters, from the tissue removed at surgery. This measurement is more accurate than the size estimated on imaging beforehand, so the two numbers may not match exactly. Size determines part of the tumor stage (pT), and the thresholds are 4 cm, 7 cm, and 10 cm. Most of these tumors are small when found. They are usually only a few centimeters across, which fits with their slow growth and favorable outlook.

Tumor extension

Tumor extension describes whether a tubulocystic renal cell carcinoma has grown outside the kidney and, if so, how far. The kidney is surrounded by a layer of fat, and outside that fat is a tough envelope called Gerota’s fascia. The adrenal gland sits atop the kidney, and the renal vein carries blood away from the kidney into the body’s largest vein, the inferior vena cava. Your pathologist examines all of these structures in the tissue removed at surgery.

The report may describe growth into the fat around the kidney (perinephric fat), into the fat in the middle of the kidney where the blood vessels enter (renal sinus fat), into the collecting system that drains urine (the pelvicalyceal system), into the renal vein, into the adrenal gland, or through Gerota’s fascia into other organs. In pure tubulocystic renal cell carcinoma, growth outside the kidney is uncommon, because most of these tumors are found while small and confined to the kidney. When extension is present, it raises the tumor stage.

Lymphovascular invasion

Lymphovascular invasion means that cells from the tubulocystic renal cell carcinoma are seen inside small blood vessels or lymphatic channels within or around the tumor. Blood vessels carry blood throughout the body, and lymphatic channels carry a fluid called lymph toward the lymph nodes. Tumor cells inside these vessels can be carried elsewhere, so lymphovascular invasion is associated with a higher risk of the cancer returning or spreading. It is uncommon in this tumor.

Lymphovascular invasion is not the same as growth into the renal vein, which is a large named vessel and is reported separately as part of tumor extension and stage. It does not change the pT stage on its own, but it is one of the findings your treatment team considers when deciding how closely to follow you after surgery.

Surgical margins

A margin is the cut edge of the tissue removed during surgery for tubulocystic renal cell carcinoma. Your pathologist examines these edges under the microscope to see whether any tumor cells reach them. Which margins are examined depends on the operation. In a partial nephrectomy, where only the tumor and a rim of surrounding tissue are removed, the margins are the kidney tissue and fat around the tumor. Partial nephrectomy is often possible for this tumor because the tumors are usually small. In a radical nephrectomy, where the whole kidney is removed, the margins include the fat around the kidney, the renal vein, and the ureter (the tube carrying urine to the bladder).

Negative margin — No tumor cells are seen at the cut edge. This suggests the whole tumor was removed and is associated with a low risk of the cancer coming back in the same place.
Positive margin — Tumor cells are present at the cut edge. This means tumor cells may have been left behind, and it is associated with a higher risk of the cancer returning at that site. A positive margin is one of the findings the surgical team uses when deciding whether more surgery or closer imaging follow-up should be considered.

Lymph nodes

Lymph nodes are small immune organs found throughout the body, including around the large blood vessels near the kidney. Cells from a tubulocystic renal cell carcinoma can travel through lymphatic channels and settle in a lymph node, although this is rare in this type of kidney cancer. Lymph nodes are not removed routinely during kidney cancer surgery. They are usually removed only when they look enlarged on imaging or feel abnormal during the operation, so many reports for this cancer will say that no lymph nodes were submitted.

If lymph nodes were removed, your report will state how many were examined, how many contained cancer, and the size of the largest deposit of tumor within a node. It may also state whether extranodal extension is present, which means that cancer cells inside a lymph node have broken through the outer capsule of the node into the surrounding tissue. Cancer in a lymph node is uncommon in this tumor, but when present it places the tumor in a higher stage group and signals a higher risk of the cancer returning.

Examination of the non-tumor kidney

When kidney tissue is removed for tubulocystic renal cell carcinoma, your pathologist also examines the kidney tissue away from the tumor. This part of the report describes how well the remaining kidney is likely to work after surgery. Common findings include scarring of the small blood vessels from long-standing high blood pressure (arterionephrosclerosis) and damage to the filters from diabetes (diabetic nephropathy). The pathologist may also note whether any papillary tumors or cysts are present in the surrounding kidney, since these are sometimes found alongside tubulocystic renal cell carcinoma. These findings do not describe the cancer itself. They are reported because they help predict kidney function after surgery.

Biomarker and molecular testing

Biomarkers are features of a tumor, usually a protein or a change in a gene, that provide information beyond the diagnosis itself. In some cancers, biomarker results decide which drug a person receives. Tubulocystic renal cell carcinoma is not one of them. No biomarker test currently selects treatment for this cancer, and most people whose tumor is removed will not have any molecular testing performed, because surgery alone is curative in almost every case. The testing described below is done in specific situations, mainly to confirm the diagnosis when the appearance is not clear-cut, or in the rare event that the cancer spreads.

Fumarate hydratase (FH) and 2SC testing

This is the most important test in tubulocystic renal cell carcinoma, and its purpose is to confirm the diagnosis rather than to guide treatment. As described in the diagnosis section, fumarate hydratase-deficient renal cell carcinoma can look very similar under the microscope but behaves in a much more concerning way and is usually inherited. The FH stain is normally present in all cells; tubulocystic renal cell carcinoma keeps it, while the fumarate hydratase-deficient tumor loses it. A second stain, 2SC, is negative in tubulocystic renal cell carcinoma and positive in the fumarate hydratase-deficient tumor. A retained FH stain together with a negative 2SC stain confirms the pure tubulocystic diagnosis. Because these stains also indicate the possibility of an inherited condition when abnormal, they carry weight beyond simply naming the tumor, which is why the pathologist reaches for them whenever the appearance leaves any doubt.

Comprehensive genomic profiling (next-generation sequencing)

Next-generation sequencing reads many genes at once from the tumor tissue. In tubulocystic renal cell carcinoma, it is generally performed only in the rare situation where the cancer has spread, and a clinical trial or a treatment outside the standard options is being considered. These tumors carry few genetic changes, so sequencing usually returns little. Reports may state which alterations were found, that no reportable alterations were identified, or that a change of uncertain significance was detected.

Mismatch repair, microsatellite instability, and tumor mutational burden

These tests identify tumors that respond to immunotherapy regardless of where the cancer started, a concept known as tumor-agnostic approval. Mismatch repair proteins (MLH1, PMS2, MSH2, and MSH6) are tested by immunohistochemistry and reported as intact or retained, which is the normal result, or as deficient (dMMR) when one or more proteins are lost. The related test for microsatellite instability is reported as stable (MSS) or high (MSI-H). Tumor mutational burden counts the number of mutations in the tumor and is reported as mutations per megabase, with 10 or more considered high. All three findings are rare in this cancer, so a normal result is expected. When one is present, it can make a person eligible for the immunotherapy drug pembrolizumab under approvals that apply across cancer types.

You can learn more about the tests described here in our Biomarkers and Genetic Testing section.

Pathologic stage (pTNM)

The pathologic stage of a tubulocystic renal cell carcinoma describes how far the cancer had grown at the time of surgery. It is written using the TNM system created by the American Joint Committee on Cancer (AJCC), currently in its 8th edition, and it is the same system used for all renal cell carcinomas. T describes the size of the tumor and how far it has grown outside the kidney, N describes whether cancer is found in nearby lymph nodes, and M describes whether the cancer has spread to a distant part of the body. The letter “p” in front means the category was assigned by a pathologist after examining the tissue. The M category is almost always determined by imaging rather than by the pathologist, so it may not appear on your report at all. Most tubulocystic renal cell carcinomas are stage pT1 at diagnosis.

Tumor stage (pT)

pT1a — The tumor is 4 cm or smaller and remains inside the kidney.
pT1b — The tumor is larger than 4 cm but not more than 7 cm and remains inside the kidney.
pT2a — The tumor is larger than 7 cm but not more than 10 cm and remains inside the kidney.
pT2b — The tumor is larger than 10 cm and remains inside the kidney.
pT3a — The tumor has grown into the renal vein or one of its branches, into the fat around the kidney or in the renal sinus, or into the collecting system that drains urine, but not beyond Gerota’s fascia.
pT3b — The tumor has grown into the inferior vena cava below the diaphragm.
pT3c — The tumor has grown into the inferior vena cava above the diaphragm, or into the wall of the vena cava.
pT4 — The tumor has grown beyond Gerota’s fascia, including growth into the adrenal gland on the same side.

Nodal stage (pN)

pN0 — No cancer was found in any of the lymph nodes examined.
pN1 — Cancer was found in one or more nearby lymph nodes.
pNX — No lymph nodes were removed or they could not be assessed. This is a common and expected result in kidney cancer surgery.

What is the prognosis?

Prognosis means the expected course of a disease. Pure tubulocystic renal cell carcinoma has one of the most favorable outlooks of any kidney cancer. It grows slowly, most tumors are small and confined to the kidney when found, and surgery cures the great majority. Reported cases of spread to other parts of the body are rare, and many were later found to have contained areas of another tumor type mixed in, which is the main reason pathologists insist on the strict “pure” definition before applying this diagnosis and its reassuring outlook.

Because the tumor is so often cured, there is no established list of report features that predict a worse outcome in the way there is for the common kidney cancers. The findings that would raise concern are the same ones that would prompt a pathologist to question whether the tumor is truly pure: solid, papillary, or sarcomatoid areas mixed in, or loss of the FH protein pointing to fumarate hydratase-deficient renal cell carcinoma instead. If your report confirms a pure tubulocystic renal cell carcinoma with retained FH, the outlook is excellent.

What happens after the diagnosis?

Once tubulocystic renal cell carcinoma has been confirmed, the findings on your pathology report, above all the confirmation that the tumor is the pure type, shape the next steps. Care usually involves a urologist, a radiologist, and a pathologist, with a medical oncologist becoming involved only in the rare event of spread.

Surgery — Surgery is the main treatment and is usually curative. A partial nephrectomy, which removes the tumor and preserves the rest of the kidney, is often possible because these tumors tend to be small. A radical nephrectomy removes the whole kidney and is considered for larger tumors. For a small tumor in an older person or someone with other health problems, active surveillance with regular imaging may also be discussed, given how slowly this tumor grows.
Treatment after surgery (adjuvant therapy) — No drug treatment after surgery is needed or recommended for pure tubulocystic renal cell carcinoma, because surgery alone is curative in almost every case. The immunotherapy options approved after kidney cancer surgery were studied in renal cell carcinoma with a clear cell component and do not apply here.
Treatment for cancer that has spread — Spread is rare enough that no treatment has been tested in a trial devoted to this cancer, and there is no established standard. In the uncommon cases that require drug treatment, options are drawn from those used for other kidney cancers, such as a drug that blocks blood vessel growth, and a clinical trial is often discussed. Chemotherapy is ineffective and not used.
Follow-up — After surgery, imaging of the abdomen and chest continues on a schedule set by your treatment team. Because the outlook is so favorable, follow-up for a pure tumor is generally less intensive than for the common kidney cancers, though it still continues for a number of years.

Questions to ask your doctor

Was my tumor confirmed to be the pure type of tubulocystic renal cell carcinoma?
Were any solid, papillary, or sarcomatoid areas found mixed in with the tubes and cysts?
Was the FH stain retained and the 2SC stain negative, ruling out fumarate hydratase-deficient renal cell carcinoma?
My report mentions a grade 3. Does that carry the same meaning it would for other kidney cancers?
How large was my tumor, and what was the pathologic stage (pT and pN)?
Did the tumor grow outside the kidney, or was it confined to the kidney?
Were the surgical margins negative or positive, and if positive, where?
Were any lymph nodes removed, and did any contain cancer?
Were any papillary tumors or cysts found in the surrounding kidney?
What did the report say about the non-tumor kidney, and how well is my remaining kidney working?
Given the favorable outlook, how often will I need imaging, and for how many years?
Do I need any treatment beyond surgery?