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Presented by Dr. Jonathan Epstein and prepared by Dr. Sintawat Wangsiricharoen
A 5.2 cm mass was noted on imaging of the prostate and was resected by a simple prostatectomy.
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1. Question
A 5.2 cm mass was noted on imaging of the prostate and was resected by a simple prostatectomy.
Choose the correct diagnosis:
Correct
Answer: B. Inflammatory myofibroblastic tumor (IMT)
Histological Description: The lesion consists of a spindle cell tumor that is destroying the prostate with residual entrapped benign prostate glands. The cells are uniform with vesicular (non-hyperchromatic) nuclei. Some of the cells have a tissue-culture appearance where the individual cells are visualized with long tapering cytoplasm on each side of the nucleus. Although frequent mitotic figures are seen, none are atypical mitoses. A sprinkling of lymphocytes and extravasated red blood cells are noted.
Discussion: The morphology in this case is typical of an IMT in its more chronic phase. Initially IMTs have a more myxoid appearance, which over time becomes less prominent. The major differential diagnosis in this case is between IMT and either a sarcomatoid carcinoma or a leiomyosarcoma. It is well known that some sarcomatoid urothelial carcinomas exhibit myxoid features mimicking IMT. IMT often expresses cytokeratin as does the spindle cells in some sarcomatoid urothelial carcinoma, making the differential diagnosis even more difficult. Finding marked cytologic atypia, atypical mitotic figures, and nonmyxoid areas with marked increased cellularity in the spindle cell areas usually allows for a diagnosis of sarcomatoid carcinoma. With the exceptionally rare cases of IMT associated with carcinoma, the most useful feature for diagnosing sarcomatoid carcinoma is the identification of an in situ or invasive epithelial component. Also, sarcomatoid carcinomas lacked ALK protein. Some leiomyosarcomas in the bladder and prostate display myxoid zones and can also express cytokeratin. The lack of a delicate vascular network, interspersed inflammatory cells and red blood cells, which are usually observed in IMT, and the presence of marked cytologic atypia, nuclear hyperchromasia, and atypical mitoses in leiomyosarcomas help in the differential diagnosis. Leiomyosarcomas and leiomyomas lack ALK protein. In the current case, ALK immunohistochemistry was diffusely positive verifying the diagnosis. However, ALK IHC may be negative in up to one-third of IMTs such that negative immunoreactivity is not helpful. IMTs are much more common in the bladder than the prostate, but can be seen in the prostate where they are identical in all respects to bladder lesions. IMTs in the male GU tract share molecular alterations with similar lesions in other sites and should be regarded as a subset of the general family of IMT rather than as pseudosarcomas. Typical IMTs can be locally aggressive, none metastasize. Typically once resected, even partially, IMTs tend to regress but they can persist in some cases requiring radical surgical resection. For these reasons, close follow-up is warranted.
References:
1. Inflammatory myofibroblastic tumors of the urinary tract: a clinicopathologic study of 46 cases, including a malignant example inflammatory fibrosarcoma and a subset associated with high-grade urothelial carcinoma. Montgomery EA, Shuster DD, Burkart AL, Esteban JM, Sgrignoli A, Elwood L, Vaughn DJ, Griffin CA, Epstein JI. Am J Surg Pathol. 2006;30:1502-12.2. ALK-1 expression in inflammatory myofibroblastic tumor of the urinary bladder. Tsuzuki T, Magi-Galluzzi C, Epstein JI. Am J Surg Pathol. 2004; 28:1609-14.
Incorrect
Answer: B. Inflammatory myofibroblastic tumor (IMT)
Histological Description: The lesion consists of a spindle cell tumor that is destroying the prostate with residual entrapped benign prostate glands. The cells are uniform with vesicular (non-hyperchromatic) nuclei. Some of the cells have a tissue-culture appearance where the individual cells are visualized with long tapering cytoplasm on each side of the nucleus. Although frequent mitotic figures are seen, none are atypical mitoses. A sprinkling of lymphocytes and extravasated red blood cells are noted.
Discussion: The morphology in this case is typical of an IMT in its more chronic phase. Initially IMTs have a more myxoid appearance, which over time becomes less prominent. The major differential diagnosis in this case is between IMT and either a sarcomatoid carcinoma or a leiomyosarcoma. It is well known that some sarcomatoid urothelial carcinomas exhibit myxoid features mimicking IMT. IMT often expresses cytokeratin as does the spindle cells in some sarcomatoid urothelial carcinoma, making the differential diagnosis even more difficult. Finding marked cytologic atypia, atypical mitotic figures, and nonmyxoid areas with marked increased cellularity in the spindle cell areas usually allows for a diagnosis of sarcomatoid carcinoma. With the exceptionally rare cases of IMT associated with carcinoma, the most useful feature for diagnosing sarcomatoid carcinoma is the identification of an in situ or invasive epithelial component. Also, sarcomatoid carcinomas lacked ALK protein. Some leiomyosarcomas in the bladder and prostate display myxoid zones and can also express cytokeratin. The lack of a delicate vascular network, interspersed inflammatory cells and red blood cells, which are usually observed in IMT, and the presence of marked cytologic atypia, nuclear hyperchromasia, and atypical mitoses in leiomyosarcomas help in the differential diagnosis. Leiomyosarcomas and leiomyomas lack ALK protein. In the current case, ALK immunohistochemistry was diffusely positive verifying the diagnosis. However, ALK IHC may be negative in up to one-third of IMTs such that negative immunoreactivity is not helpful. IMTs are much more common in the bladder than the prostate, but can be seen in the prostate where they are identical in all respects to bladder lesions. IMTs in the male GU tract share molecular alterations with similar lesions in other sites and should be regarded as a subset of the general family of IMT rather than as pseudosarcomas. Typical IMTs can be locally aggressive, none metastasize. Typically once resected, even partially, IMTs tend to regress but they can persist in some cases requiring radical surgical resection. For these reasons, close follow-up is warranted.
References:
1. Inflammatory myofibroblastic tumors of the urinary tract: a clinicopathologic study of 46 cases, including a malignant example inflammatory fibrosarcoma and a subset associated with high-grade urothelial carcinoma. Montgomery EA, Shuster DD, Burkart AL, Esteban JM, Sgrignoli A, Elwood L, Vaughn DJ, Griffin CA, Epstein JI. Am J Surg Pathol. 2006;30:1502-12.2. ALK-1 expression in inflammatory myofibroblastic tumor of the urinary bladder. Tsuzuki T, Magi-Galluzzi C, Epstein JI. Am J Surg Pathol. 2004; 28:1609-14.
