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Presented by Dr. Pedram Argani and prepared by Dr. Katherine Fomchenko
This is a middle-aged female with a renal mass.
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1. Question
This is a middle-aged female with a renal mass. WT1 and ALK immunostains are included.
WT1:
ALK:
Correct
Answer: C. ALK rearranged renal cell carcinoma
Histologic Description: This is an extremely unusual and illustrative case. Morphologically, most of the lesion looks like metanephric adenoma in that it is composed of small tubules formed by blue cells with minimal cytoplasm arranged in a hyalinized stroma, given a “fingerprint” like appearance. This morphology merges with areas with more overt papillary architecture, more open chromatin, and large areas of necrosis with neutrophilic infiltrate, some of which could be due to a prior biopsy. By immunohistochemistry, the lesion demonstrates patchy nuclear labeling for WT1, but also demonstrates patchy immunoreactivity for ALK protein. The neoplasm demonstrates an ALK gene rearrangement.
Differential Diagnosis: Metanephric adenoma fits the morphology of much of this case, though the more open chromatin in the slightly more papillary areas would be unusual. Metanephric adenoma-Wilms tumor composite is a consideration given the necrosis; however, there are no areas that diagnostic of epithelial Wilms tumor such as areas of tubule formation with columnar nuclei with mitotic activity. Metanephric adenomas do not typically form composite tumors with papillary renal cell carcinomas since they arise by different genetic pathways (BRAF mutation in metanephric adenoma, trisomy chromosome 7/17 in low grade papillary carcinoma) unless they are both associated with metanephric stromal tumor. There is no evidence of metanephric stromal tumor in this case. This case demonstrates the wide spectrum which may be seen in renal cell carcinoma associated with ALK rearrangement. Cases similar to this with rearrangement of ALK have been reported recently.
Reference:
International Journal of Surgical Pathology 2021; 29:808-814 (PMID: 33729862)
Modern Pathology 2020; 33:2563-2579 (PMID: 32467651).
Incorrect
Answer: C. ALK rearranged renal cell carcinoma
Histologic Description: This is an extremely unusual and illustrative case. Morphologically, most of the lesion looks like metanephric adenoma in that it is composed of small tubules formed by blue cells with minimal cytoplasm arranged in a hyalinized stroma, given a “fingerprint” like appearance. This morphology merges with areas with more overt papillary architecture, more open chromatin, and large areas of necrosis with neutrophilic infiltrate, some of which could be due to a prior biopsy. By immunohistochemistry, the lesion demonstrates patchy nuclear labeling for WT1, but also demonstrates patchy immunoreactivity for ALK protein. The neoplasm demonstrates an ALK gene rearrangement.
Differential Diagnosis: Metanephric adenoma fits the morphology of much of this case, though the more open chromatin in the slightly more papillary areas would be unusual. Metanephric adenoma-Wilms tumor composite is a consideration given the necrosis; however, there are no areas that diagnostic of epithelial Wilms tumor such as areas of tubule formation with columnar nuclei with mitotic activity. Metanephric adenomas do not typically form composite tumors with papillary renal cell carcinomas since they arise by different genetic pathways (BRAF mutation in metanephric adenoma, trisomy chromosome 7/17 in low grade papillary carcinoma) unless they are both associated with metanephric stromal tumor. There is no evidence of metanephric stromal tumor in this case. This case demonstrates the wide spectrum which may be seen in renal cell carcinoma associated with ALK rearrangement. Cases similar to this with rearrangement of ALK have been reported recently.
Reference:
International Journal of Surgical Pathology 2021; 29:808-814 (PMID: 33729862)
Modern Pathology 2020; 33:2563-2579 (PMID: 32467651).
