It is a malignant tumor having papillary and tubulopapillary architecture with tumor cells having origin from renal tubular epithelial cells
Incidence – 10-15% of all RCC
Sex- Predominance in males (with male to female ration of 2:1)
Age – early adulthood to oldage
Etiology – No specific etiological factors but found to be associated with acquired cystic disease and end stage renal disease with scarring. Some cases are found to be associated with syndromes
Genetics – common chromosomal abnormality is trisomy or tetrasomy of 7 and 17
Bilaterality and multifocality is common in this tumor
Morphology
Gross-
Grossly tumors are well circumscribed and are situated eccentrically in renal cortex
In few cases distinct fibrous capsule may be seen
Cut surface may be gray to red brown granular or golden yellow due to lipid laden macrophages in the stroma
Intratumoral hemorrhage and necrosis may be present in 2/3rds of cases
These tumors are usually associated with cortical adenoma or can present in wall of cyst
They are often multiple
Numerous tumors are seen in hereditary type RCC
Microscopically :
Papillary RCC is usually surrounded by fibrous capsule
Tumor is characterised by papillae having fibrovascular stalks lined by single layered or pseudo stratified layers of tumor cells
Most of the tumor shows papillae but in some case tubules may also be seen
Tightly packed papillae and tubules may give solid appearance
Accumulation of foam cells or xanthoma cells or lipid laden macrophages in the papillary stalk is characteristic
Papillary cores are expanded and can be hyalinised or thickened
Tumor necrosis and psammomatous calcification may be seen
Mucin secretion is seen in small percentage of cases
Tumor cells are basophilic, amphophilic and clear
Papillary RCC has been separated into two subtypes based on morphologic features by Delahunt and Eble
Type-1
Type 2
Type-1 tumors:
Constitutes 2/3rds of cases
Composed of small cells having scanty basophilic or pale cytoplasm
Nuclei are small and ovoid with inconspicuous nucleoli (Grades 1& 2)
Nuclear grooves may be seen
Cells form single layer on papillae
Foamy macrophages and psammoma bodies are abundant
Type -2 tumors:
Constitutes less than 1/3rd of cases
Composed of large cells with abundant acidophilic cytoplasm
Cytoplasmic clearing is typically apical
Nuclei are large spherical with prominent nucleoli (grade3)
Focal pseudo stratification of cells are seen
Few cells may show intracytoplasmic lumen
In cases with mixture of two types, classification is dependent on the predominant type
Hereditary papillary RCC’s are composed of small cells with scant basophilic cytoplasm & low grade nuclei. Areas of haemorrhages necrosis,psammoma bodies and numerous foamy macrophages are seen.
Immunohistochemical findings
Tumor cells are strongly positive for – Pancytokeratins, Low molecular weight cytokeratin antibodies
Type1 tumors – strongly reactive for Cytokeratin 7 than type2 tumors
Tumor cells are positive for-
Vimentin
CD9
CD10
Parvalbumin
Beta-defensin1
Few tumors are reactive for CEA
Prognosis
papillary RCC’s have better prognosis than clear cell type
Type 1 has better prognosis than type 2 type
These tumors have propensity for metatsasis and late recurrence
Differential diagnosis
Papillary adenoma
Size of tumor is less than 5mm
tumor shows tubulopapillary architecture line by cells having scant amphophilic to basophilic cytoplasm and low grade nuclei
Immunohistochemistry – Cells are positivr for AMACR, CK 7, EMA and high molecular weight cytokeratins
Clear cell papillary RCC
Clear cells are cytologically low grade showing reverse polarity with subnuclear clearing and linear arrangement of nuclei
More solid and nested areas are seen with areas of papillary tufts
Immunohistochemistry –
Strong positivity with CK 7
CD 10 and Racemase are typically negative
PAX 8 and high molecular weight keratin are often positive
Metanephric adenoma
Benign tumor with female predominance showing tightly packed primitive tubules and acini intermingled with papillary or glomeruloid structures
Tumor cells are small and uniform with round to oval nuclei, inconspicuous nucleoli and absent or rare mitosis
Immunohistochemistry
Positive for – WT 1, PAX 2, CD57
Negative for – CK7, CD56, AMACR
Reference
William M.Murphy ,David J.Grignon,ElizabethJ.Perlman. Renal cell carcinoma,papillary type . In tumors of the kidney ,bladder and related urinary structures.AFIP atlas odf tumor pathology.Series 4.123-129
John N.Eble,Robert H.Young.TUmors of urinary tract. In diagnostic histopahology of tumors by Christopher.D.M. Fletcher.Third edition Volume1.485-566.
Mario F.Serrano and peter A.Humphrey .Adult renal neoplasms.In surgical diseases of kidney.The Washington manual of surgical pathology.By: peterA.Humphrey,Louis P.Dehner John D.Pfeifer.second edition 2016.357-371