Papillary Adenoma of the Kidney: Understanding Your Pathology Report

Section Editor: Trevor Flood MD FRCPC
July 19, 2026

Papillary adenoma is a small, benign (noncancerous) tumor of the kidney. It arises from the tiny tubes inside the kidney called tubules, and it grows in small finger-like projections called papillae, sometimes in small tubes, or in a mixture of the two. It is one of the most common tumors found in the kidney, and it does not spread to other parts of the body.

The most important thing to understand about papillary adenoma is how it is usually found. It is almost never the reason for surgery. Instead, it is a small, harmless finding that a pathologist notices in kidney tissue removed for some other reason, or in the kidney tissue around a larger tumor. If your report mentions one or more papillary adenomas, this is an incidental finding and not a second cancer.

This article will help you understand the findings in your pathology report for papillary adenoma of the kidney, what each term means, and why it matters for your care.

What causes papillary adenoma?

The exact cause of a papillary adenoma, a common benign kidney tumor, is not known, but several situations make it more likely. They become more common with age and are frequently found in the kidneys of older adults. They are strongly associated with long-standing kidney disease, particularly in people on dialysis for many years and those who develop cysts in the kidneys (acquired cystic kidney disease). They are also more common in kidneys damaged by disease of the small blood vessels or the filtering units (glomeruli). Papillary adenomas are thought to arise from the same process that gives rise to papillary renal cell carcinoma, and they are widely regarded as a possible early step toward that cancer, although the great majority never progress. They share the same genetic changes, most often extra copies of chromosomes 7 and 17.

Inherited conditions

Most papillary adenomas are not inherited. Uncommonly, multiple papillary adenomas occur in people with hereditary papillary renal cell carcinoma, an inherited condition caused by a change in the MET gene. Finding several papillary adenomas, particularly in a younger person, may warrant consideration of an inherited condition.

What are the symptoms of papillary adenoma?

Papillary adenomas cause no symptoms. Because they are so small, they do not cause pain, blood in the urine, or other problems associated with larger kidney tumors. They are found by chance, either in kidney tissue removed for another reason or, occasionally, as a tiny spot noted on imaging. A papillary adenoma is not something a person feels or notices.

How is the diagnosis made?

The diagnosis of papillary adenoma is made by a pathologist examining kidney tissue under the microscope. Unlike most tumors described on this site, a papillary adenoma is almost never the target of a procedure. It is usually discovered incidentally, most often in the kidney tissue surrounding a larger tumor that was removed, in a kidney removed for another disease, or sometimes in a biopsy taken for a different reason. Because it is so small and causes no symptoms, it is rarely, if ever, removed on its own.

Under the microscope, a papillary adenoma is made up of small, uniform cells arranged along papillae built around thin cores of connective tissue and blood vessels (fibrovascular cores), in small tubes, or in a mixture of the two. The cells are even in size and shape, with pale interiors and small, regular nuclei, and they rarely divide. Two additional findings are common and may be mentioned in the report: foamy histiocytes, which are immune cells filled with fat, and psammoma bodies, which are tiny round deposits of calcium. A papillary adenoma lacks a capsule, so it blends gradually with the surrounding kidney. Like papillary renal cell carcinoma, it is usually positive for AMACR and often for CK7, but these stains do not distinguish an adenoma from that cancer; the distinction rests on size and grade, as described in the next section.

How papillary adenoma is defined: size, grade, and the border with cancer

Papillary adenoma and papillary renal cell carcinoma are composed of similar-looking cells, and under the microscope, a papillary adenoma resembles a very small, low-grade papillary renal cell carcinoma. What separates them is not a difference in the cells alone but a set of specific rules, and it is worth understanding them because they explain why a tumor is called one thing rather than the other.

The World Health Organization, which sets the rules pathologists follow, defines a papillary adenoma by three features that must all be present:

Size 15 mm or smaller — The lesion must measure no more than 15 millimeters (about 0.6 inches) across. A lesion with the same appearance that is larger than 15 mm is classified as papillary renal cell carcinoma.
Low grade — The nuclei must be low grade, meaning the nucleoli inside them are not easily seen. A lesion with high-grade nuclei is not called a papillary adenoma even if it is small.
No capsule — The lesion must be unencapsulated, blending into the surrounding kidney rather than being surrounded by a wall.

The 15 mm size limit is not arbitrary. It was chosen because lesions at or below this size, with low-grade nuclei, have not been observed to spread to other parts of the body. In other words, the definition draws the line exactly where the risk of harmful behavior begins, which is why a lesion meeting all three rules can be called benign with confidence. This is also the reason a kidney containing only papillary adenomas can still be used for transplantation: the adenomas pose no meaningful risk to the recipient.

What if more than one is found?

More than one papillary adenoma is often present, especially in kidneys affected by long-standing disease. When many are found throughout the kidney, the condition is sometimes called renal adenomatosis. Having several papillary adenomas does not make them cancerous or change their benign nature. It can, however, be a reason to consider whether an underlying condition, such as chronic kidney disease or, less commonly, an inherited condition, is present.

Is papillary adenoma staged?

Papillary adenoma is not given a stage. Staging systems, such as the TNM system, are used to describe how far cancer has grown and spread. Because a papillary adenoma is benign and does not spread, there is no stage to assign, and no grade is reported for it beyond confirming that its nuclei are low grade, which is part of the definition.

What is the prognosis?

Prognosis means the expected course of a disease. For papillary adenoma, the outlook is excellent. It is benign, it does not spread, and it is not life-threatening. A papillary adenoma does not interfere with how the kidney works, and finding one, or several, does not by itself require any treatment. Because these lesions share their biology with papillary renal cell carcinoma and are considered a possible early step toward it, a person found to have papillary adenomas, particularly alongside other kidney disease, may have their kidneys monitored over time, but the adenomas themselves are not treated.

What happens after the diagnosis?

Because a papillary adenoma is almost always an incidental finding, the diagnosis usually does not warrant treatment directed at the adenoma itself. What happens next depends far more on the reason the kidney tissue was examined in the first place.

No treatment for the adenoma — A papillary adenoma does not need to be removed or treated. When it is found in tissue already removed for another reason, nothing further is required for the adenoma.
Follow-up of the kidneys — If you have long-standing kidney disease, are on dialysis, or have several papillary adenomas, your kidneys may be monitored with periodic imaging. This is aimed at your overall kidney health and at watching for any larger tumor developing, rather than at the adenoma itself.
Genetic assessment — If several papillary adenomas are found, particularly in a younger person or alongside a papillary renal cell carcinoma, a referral to a genetics clinic may occasionally be considered to look for an inherited condition such as hereditary papillary renal cell carcinoma.

Questions to ask your doctor

Was the papillary adenoma an incidental finding, or was it the reason for my procedure?
How was it confirmed to be a papillary adenoma rather than a papillary renal cell carcinoma?
How large was it, and were the nuclei low grade?
Was more than one papillary adenoma found?
Does this finding affect my kidney function?
Do I need any treatment or follow-up because of it?
Should my kidneys be monitored over time, and if so, how often?
Could several papillary adenomas suggest an inherited condition, and should my family be considered?
If this was found in a kidney being considered for donation, does it affect the transplant?
What symptoms, if any, should prompt me to seek medical attention?