Pseudosarcomatous myofibroblastic proliferations of the genitourinary tract are genetically different from nodular fasciitis and lack USP6, ROS1 and ETV6 gene rearrangements

USP6-associated neoplasm as a tentative subset of postoperative spindle cell nodule

AIM

Postoperative spindle cell nodule (PSCN) is a pseudosarcomatous proliferative lesion of unclear molecular genetic origins.

METHODS AND RESULTS

We examined seven patients with PSCN, using routine haematoxylin-eosin (H&E) slide preparations and a series of immunostains. The latter targeted keratin, vimentin, α-smooth muscle actin (SMA), anaplastic lymphoma kinase (ALK [D5F3]), and other proteins. Ubiquitin-specific peptidase 6 (USP6) and anaplastic lymphoma kinase (ALK) gene rearrangements were also analysed by fluorescence in situ hybridization (FISH). There were histories of prior surgical intervention (n = 6) or trauma (n = 1) in all seven patients. All lesions were highly cellular and mitotically active spindle cell proliferations, with no cytologic atypia, nuclear pleomorphism, or aberrant mitoses. Immunohistochemical (IHC) staining disclosed focal, weak keratin positivity in two lesions, whereas vimentin (diffuse, strongly positive) and SMA (tram-track pattern) were present in each instance, and ALK (D5F3) was entirely negative. FISH analysis confirmed USP6 gene rearrangements in all seven cases, showing no ALK gene rearrangements. RNA sequencing results showed an MYH9::USP6 gene fusion in only one lesion (No. 6).

CONCLUSION

A subset of PSCN is marked by USP6 gene rearrangements, a genetic feature of nodular fasciitis (NF). Given its similarity to NF, a designation as USP6-associated neoplasm (UAN) seems reasonable, signifying a transient clonal neoplastic lesion.

Case report: Large-size intramuscular nodular fasciitis, a challenging histopathologic diagnosis confirmed by molecular detection of USP6 gene rearrangement: Case report and literature review

The intramuscular subtype of nodular fasciitis (NF) is rare with lesions normally not more than 2 cm in size and characterized by pseudosarcomatous morphology. We report a case of a 27-year-old man with a large-size intramuscular NF. The patient came for treatment complaining of an increasingly enlarged mass in the left upper arm for 4 months. Magnetic resonance imaging (MRI) confirmed the presence of a well-defined tumor measuring 5 cm within the outer edge of the middle humerus. Microscopically, the neoplasm was rich in fibroblasts and myofibroblasts in an interlaced pattern with high mitotic index and evident multinuclear giant cells. Erythrocyte extravasation was easily seen in the stroma. The tumor border was infiltrative. Immunohistochemically, the tumor cells were positive for smooth muscle actin (SMA) and negative for cytokeratin, desmin, H-Caldesmon, CD34, S100, ALK, and β-catenin. Fibrosarcoma was highly suspected by histopathological and immunohistochemical examination. Molecular detection demonstrated evidence of ubiquitin-specific peptidase 6 (USP6) gene rearrangement in this tumor. Based on the findings, the tumor was diagnosed as intramuscular NF. At 56 months after the initial surgery, the patient had recovered with no evidence of recurrence or metastasis. Large-size intramuscular NF is very rare and easily overdiagnosed as malignant tumor due to its obvious pseudosarcomatoid pathological features. USP6 gene rearrangement detection can effectively avoid this major misdiagnosis.

Clinicopathological analysis and outcomes of inflammatory myofibroblastic tumours of the urinary bladder

OBJECTIVES

To describe clinical, imaging, and histopathological characteristics of inflammatory myofibroblastic tumour (IMT) of the urinary bladder and provide initial management and surveillance recommendations.

PATIENTS AND METHODS

We identified patients with IMT of the bladder treated at our facility from 1998 to 2020. Categorical variables were analysed with chi-square and Fisher's exact tests and continuous variables with the Mann-Whitney U-test. Kaplan-Meier analysis was performed for recurrence-free survival.

RESULTS

IMT was diagnosed in 35 patients with median (interquartile range [IQR]) follow-up of 20 (11.5-68.5) months. At initial diagnosis 86% were clinically organ-confined, 9% locally advanced, and 5% metastatic. Majority of patients (92%) had residual disease on re-staging transurethral resection (TUR). Of the 15 patients with organ-confined disease managed initially with TUR alone, five (33%) recurred at a median (IQR) of 5 (3.0-5.5) months from initial diagnosis. Presentation with visible haematuria was associated with recurrence (100% in recurrence vs 40% in non-recurrence groups, P = 0.044). There were no patients who developed a recurrence beyond 6 months after diagnosis. Partial or radical cystectomy was required in 23% and 9% of patients, respectively. One patient presented with metastatic disease associated with anaplastic lymphoma kinase (ALK) translocation and achieved a durable complete remission with 7 months of crizotinib therapy.

CONCLUSIONS

No patient with IMT treated with aggressive endoscopic management developed recurrences beyond 6 months. There were additionally no recurrences noted after definitive radical or partial cystectomy. These data support organ sparing therapy with aggressive endoscopic management and short-term surveillance in patients with localised IMT, with extirpative surgery reserved for refractory cases.

Mimickers of Urothelial Carcinoma and the Approach to Differential Diagnosis

A broad spectrum of lesions, including hyperplastic, metaplastic, inflammatory, infectious, and reactive, may mimic cancer all along the urinary tract. This narrative collects most of them from a clinical and pathologic perspective, offering urologists and general pathologists their most salient definitory features. Together with classical, well-known, entities such as urothelial papillomas (conventional (UP) and inverted (IUP)), nephrogenic adenoma (NA), polypoid cystitis (PC), fibroepithelial polyp (FP), prostatic-type polyp (PP), verumontanum cyst (VC), xanthogranulomatous inflammation (XI), reactive changes secondary to BCG instillations (BCGitis), schistosomiasis (SC), keratinizing desquamative squamous metaplasia (KSM), post-radiation changes (PRC), vaginal-type metaplasia (VM), endocervicosis (EC)/endometriosis (EM) (müllerianosis), malakoplakia (MK), florid von Brunn nest proliferation (VB), cystitis/ureteritis cystica (CC), and glandularis (CG), among others, still other cellular proliferations with concerning histological features and poorly understood etiopathogenesis like IgG4-related disease (IGG4), PEComa (PEC), and pseudosarcomatous myofibroblastic proliferations (post-operative spindle cell nodule (POS), inflammatory myofibroblastic tumor (IMT)), are reviewed. Some of these diagnoses are problematic for urologists, other for pathologists, and still others for both. Interestingly, the right identification of their definitory features will allow their correct diagnoses, thus, avoiding overtreatment. The literature selected for this review also focuses on the immunohistochemical and/or molecular data useful to delineate prognosis.

Pseudosarcomatous myofibroblastic proliferations of the urinary bladder are neoplasms characterized by recurrent FN1-ALK fusions

Pseudosarcomatous myofibroblastic proliferation is a descriptive term that designates a group of clinically indolent genitourinary lesions that most commonly arise in the urinary bladder. Given that pseudosarcomatous myofibroblastic proliferation may show morphologic overlap with inflammatory myofibroblastic tumor, the relationship, if any, between the two entities has been unclear. Moreover, pseudosarcomatous myofibroblastic proliferations are known to be positive for ALK immunohistochemistry in a subset of cases, although an inconsistent association with ALK rearrangement (ranging from 0 to 60%) has been reported. The objectives of this study were to determine the frequency of ALK rearrangement and to identify fusion partners using fluorescence in situ hybridization (FISH) and targeted RNA sequencing studies in a contemporary series of 30 pseudosarcomatous myofibroblastic proliferations of the urinary bladder, as well as to investigate ROS1 status by immunohistochemistry. ALK immunohistochemistry was positive in 70% (21/30) of pseudosarcomatous myofibroblastic proliferations; ROS1 immunohistochemistry was consistently negative (0/28). ALK rearrangements were detected by FISH in 86% (18/21) of cases, correlating with ALK immunohistochemical positivity in all but 3 cases. Of eight cases confirmed to be ALK rearranged by FISH, targeted RNA-sequencing detected FN1-ALK fusions in seven (88%) cases, which involved exons 20-26 of FN1 (5') and exon 18-19 of ALK (3'). In conclusion, ALK rearrangements are frequent in pseudosarcomatous myofibroblastic proliferations, typically involving exon 19, and FN1 appears to be a consistent fusion partner. Given the significant clinicopathologic differences between inflammatory myofibroblastic tumor and pseudosarcomatous myofibroblastic proliferation, our findings provide further support for classification of pseudosarcomatous myofibroblastic proliferation as a distinct clinicopathologic entity, and propose the alternate terminology "pseudosarcomatous myofibroblastic neoplasm of the genitourinary tract."

TERT promoter mutation analysis as a surrogate to morphology and immunohistochemistry in problematic spindle cell lesions of the urinary bladder

AIMS

Pseudosarcomatous myofibroblastic proliferations (PSMPs) of the urinary bladder are diagnostically challenging. Diagnostic difficulties are mainly due to frequent cytokeratin expression, variable ALK expression and worrisome morphological features suggestive of malignancy. Conversely, sarcomatoid urothelial carcinoma (UC) may show bland inflammatory myofibroblastic tumour (IMT)-like morphology. TERT promoter mutations are characteristic events in urothelial cancers, but have not been studied in PSMPs.

METHODS AND RESULTS

We compared histomorphological and immunohistochemical features and TERT promoter status in 16 PSMPs and 18 sarcomatoid UC. In a subset of PSMPs, RNA sequencing was performed. At least focal IMT-like morphology was seen in nine of 17 sarcomatoid UC. Atypical mitoses, differentiated urothelial component and heterologous elements were the most reliable distinguishing histomorphological features of sarcomatoid UC, if present. A panel of immunohistochemistry (IHC) including ALK (clone D5F3), p53 pattern, p63 and GATA3 reliably distinguished PSMP from sarcomatoid UC. GATA3 (P = 0.001) and p53 patterns (mutant versus wild-type; P < 0.001) were differentially expressed between PSMPs and sarcomatoid UC. Diffuse pancytokeratin staining was significantly associated with PSMPs (10 of 13) compared to four of 14 sarcomatoid UCs (P = 0.012). TERT promoter mutations were found in 17 of 18 sarcomatoid UC versus none of 16 PSMPs (P < 0.001). RNA sequencing revealed ALK genetic rearrangements in one of two ALK-positive and one of 10 ALK-negative PSMPs, which revealed a novel FN1/RET gene fusion.

CONCLUSION

Careful histomorphological analysis and differential IHC reliably distinguish the majority of PSMPs and sarcomatoid UC. In equivocal cases, TERT promoter mutation analysis and/or detection of ALK expression/rearrangements are valuable additional diagnostic adjuncts, strongly supporting sarcomatoid UC and PSMP, respectively.

Gene fusion characterisation of rare aggressive prostate cancer variants-adenosquamous carcinoma, pleomorphic giant-cell carcinoma, and sarcomatoid carcinoma: an analysis of 19 cases

AIMS

To evaluate the molecular underpinnings of the rare aggressive prostate cancer variants adenosquamous carcinoma, pleomorphic giant-cell carcinoma, and sarcomatoid carcinoma.

METHODS AND RESULTS

We retrieved 19 tumours with one or more variant(s), and performed ERG immunohistochemistry, a next-generation sequencing assay targeting recurrent gene fusions, and fluorescence in-situ hybridisation (FISH) for ERG and BRAF. Divergent differentiation included: sarcomatoid carcinoma (n = 10), adenosquamous carcinoma (n = 7), and pleomorphic giant-cell carcinoma (n = 7). Five patients had more than one variant. Four had variants only in metastases. ERG rearrangement was detected in nine (47%, seven via sequencing, showing TMPRSS2-ERG fusions and one GRHL2-ERG fusion, and two via FISH, showing rearrangement via deletion). ERG was immunohistochemically positive in the adenocarcinoma in eight of nine (89%) patients, but was immunohistochemically positive in the variant in only five of nine patients (56%, typically decreased). One patient had a false-positive ERG immunohistochemical result in the sarcomatoid component despite a negative FISH result. Two (11%) harboured BRAF fusions (FAM131A-BRAF and SND1-BRAF).

CONCLUSIONS

ERG fusions are present in these rare prostate cancer variants with a frequency close to that in conventional prostate cancer (9/19, 47%). ERG immunohistochemistry usually detects rearrangement in the adenocarcinoma, but is less sensitive for the variant histology, with weak to negative staining. Adenosquamous and sarcomatoid variants can, particularly, occur together. Molecular assessment may be an additional tool in selected cases to confirm the prostatic origin of unusual tumours. The presence of two BRAF rearrangements suggests that this gene fusion may be enriched in this setting, as RAF kinase fusions have been previously reported in 1-2% of prostate cancers.

Sclerosing TSC1 mutated renal cell carcinoma: An unusual pattern mimicking MITF family translocation renal cell carcinoma

The tuberous sclerosis genes and MTOR are increasingly being found to have important roles in novel subtypes of renal cancer, particularly emerging entities eosinophilic solid and cystic renal cell carcinoma (RCC) and high-grade oncocytic renal tumor (HOT)/RCC with eosinophilic and vacuolated cytoplasm. We report a unique renal neoplasm in a 66-year-old woman that initially mimicked MITF family translocation RCC due to mixed clear and eosinophilic cells, extensive stromal hyalinization, and psammoma bodies, yet which was negative for TFE3 and TFEB fluorescence in situ hybridization and a next generation sequencing (NGS) gene fusion assay. Cytoplasmic stippling triggered consideration of TSC-associated neoplasms, and a targeted NGS assay revealed a variant in exon 21 of TSC1 resulting in c.2626G>T p.(Glu876*) truncating mutation. This report adds to the morphologic spectrum of TSC-related renal neoplasms, including prominent stromal hyalinization as a potentially deceptive pattern. Due to the overlap in cytoplasmic stippling between eosinophilic solid and cystic RCC and HOT/RCC with eosinophilic and vacuolated cytoplasm, it is debatable which category this example would best fit. Further understanding of these entities and other renal neoplasms with alterations in the TSC genes will elucidate whether they should be considered a family of tumors.

A Novel COL1A1-CAMTA1 Rearrangement in Cranial Fasciitis

Cranial fasciitis is an uncommon benign fibroblastic tumor, generally histologically identical to nodular fasciitis. It develops almost exclusively in children. Cranial fasciitis manifests clinically as a painless rapidly growing solitary nodule in the head and neck area, frequently eroding the underlying bone. Thus, this entity is often confused with aggressive lesions such as sarcomas, both clinically and radiologically. Histopathologic examination is essential to differentiate between cranial fasciitis and fibrohistiocytic or even sarcomatous lesions observed in children. In this article, we present a case of cranial fasciitis with intracranial extension in a 2-year-old boy. Although USP6 rearrangement has recently been recognized as a recurring alteration in nodular fasciitis, we present a novel COL1A1-CAMTA1 fusion in this lesion.