Kidney tumor

• Papillary adenoma is a benign kidney lesion defined by the IARC: WHO Classification of Tumours of the Urinary System and Male Genital Organs (Medicine), 4th Edition, 2016 as an unencapsulated tumor with papillary or tubular architecture, low WHO / ISUP grade and a diameter of ≤ 15 mm (Eur Urol 2016;70:93)

• Benign papillary and tubulopapillary, low nuclear grade lesions of the kidney similar in morphology to papillary renal cell carcinoma type 1, however, lack pseudocapsule and are ≤ 15 mm
• Based on available data, these lesions do not have the capability to metastasize
• Prevalent in damaged and injured kidneys and could be related to a progenitor / stem cell-like renal tubular cell population that is increased upon kidney damage
• Papillary adenomas are postulated to be precursor lesions to papillary renal cell carcinoma (RCC), however, the adenomas prevalence is much higher than carcinomas, indicating that many of them do not progress

• Prior synonym: renal cortical adenoma
• Renal adenomatosis for bilateral and multifocal cases

• Reported in 7% of kidneys resected for other tumors, they are more frequent in resected kidneys accompanying RCC, papillary type compared with other subtypes (Hum Pathol 2007;38:239)
• Present in 7 - 40% of autopsy studies, frequency increases with age (Hum Pathol 2007;38:239, Am J Surg Pathol 2019;43:277)
• Higher incidence in patients with chronic kidney disease, similar to papillary RCC (Int Urol Nephrol 2014;46:2127, Virchows Arch 2008;453:313, Transplant Proc 2008;40:3354)

• Renal cortex

• Studies hypothesize that the origin is renal tubular progenitor / stem cells (Am J Pathol 2019;189:2046)
• Renal tubular progenitor / stem cells increase upon renal injury or damage (Int Urol Nephrol 2014;46:2127)
• Progenitor cells give rise to papillary adenoma, which in turn could be precursors to papillary RCC (Virchows Arch 2008;453:313, Am J Pathol 2011;178:828)

• Unknown, possibly secondary to renal injury as chronic medical renal diseases, pyelonephritis or nearby mass tumor effect (Am J Pathol 2019;189:2046 )

• Incidentally found in nephrectomies removed for larger tumors or other causes
• More common in kidneys harboring papillary RCC (> 25%), compared with other types of renal tumors
• Very common in end stage kidneys (Int Urol Nephrol 2014;46:2127, Virchows Arch 2008;453:313, Transplant Proc 2008;40:3354)

• Imaging: usually CT scan, ≤ 15 mm, often not seen
• Diagnosis by biopsy or resection, however, diagnosis on needle biopsy should be made with caution as capsule and grade heterogeneity may not be visualized (Eur Urol 2016;70:93)

• Difficult to differentiate from other lesions using imaging

• Benign lesions, thought to be precursor lesions of papillary RCC, however, the incidence of papillary RCC is much lower than papillary adenoma, indicating that not all cases have the potential to progress (Am J Pathol 2019;189:2046)
• Size criterion changed from 5 mm to 15 mm in the WHO 2016 classification based on data that these lesions have no capacity to metastasize
• Change allows for increased acceptance of donor kidney for transplantation, in which kidneys with papillary lesions ≤ 15 mm would not be rejected (Eur Urol 2016;70:93)

• 41 year old man with autosomal dominant polycystic kidney disease and renal papillary adenomas presented with unusual clinical presentation (Iran J Kidney Dis 2013;7:439)
• 57 year old man with unusual imaging presentation of a papillary adenoma (Hinyokika Kiyo 2001;47:865)

• Treatment is based on the presenting tumor or condition
• Considered benign; does not, on its own, require treatment

• Depending on lesion size, smaller lesions might not be visible, larger lesions appear as well circumscribed, usually subcapsular, grayish-white to yellow nodules

AFIP images

Contributed by Rola Saleeb, M.D., Ph.D.


Contributed by Hsin-Yi Chang, M.D. and Jen-Fan Hang, M.D.

• CK7, AMACR (similar to papillary RCC)

• CAIX (positive in clear cell RCC)

• Trisomy 7 and 17, loss of Y (very frequent); often gains of chromosomes 12, 16 and 20 (similar to papillary RCC) (Hum Pathol 2007;38:239, Mod Pathol 2003;16:1053)
• Similar chromosomal changes molecular profiles to end stage kidneys (Am J Pathol 2019;189:2046, Virchows Arch 2008;453:313)

Images hosted on other servers:

• Papillary renal cell carcinoma:
  • Size larger than 15 mm
  • Capsule is present or high grade morphology

A 38 year old woman with recurrent pyelonephritis was found to have a 1 cm left renal mass on imaging. A biopsy of the lesion was performed that showed this morphology. Which of the following is the correct diagnosis and WHO / ISUP grade?


1. Papillary adenoma WHO / ISUP grade 2
2. Papillary adenoma, not graded
3. Papillary renal cell carcinoma WHO / ISUP grade 1
4. Papillary renal cell carcinoma WHO / ISUP grade 2

B. Papillary adenomas are low grade lesions by morphology, however they are considered benign and are not graded as per the current guidelines

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Reference: Papillary adenoma

What are the chromosomal aberrations reported in papillary adenoma lesions?


1. Trisomies of 7 and 17 only
2. Trisomies of 7, 17 and loss of Y and less frequently gains in chromosomes 12, 16 and 20
3. Trisomies of 7, 17 and loss of Y as well as deletions of the short arm of chromosome 3

B. Papillary adenomas show chromosomal aberrations similar to papillary renal cell carcinoma, which include trisomies of chromosomes 7, 17, loss of Y and occasional gains in 12, 16 and 20. Chromosome 3p deletions are common in clear cell renal cell carcinoma

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Reference: Papillary adenoma