Emerging concepts in micropapillary urothelial carcinoma

Current Advances in the Management of Nonurothelial Subtypes of Bladder Cancer

Urothelial cancer (UC) is the most common histology seen in bladder tumors. The 2022 WHO classification of urinary tract tumors includes a list of less common subtypes (formerly known as variants) for invasive UC which are considered high-grade tumors. This review summarizes the most recent advances in the management of selected nonurothelial subtypes of bladder cancer: squamous cell carcinoma, small cell carcinoma, sarcomatoid urothelial carcinoma, micropapillary carcinoma, plasmacytoid carcinoma, adenocarcinoma, and urachal carcinoma. The role of neoadjuvant and adjuvant chemotherapy has not been well characterized for most of these histologies, and prospective data are extremely limited. Participation in clinical trials is recommended in advanced disease.

Clinicopathological Review of Micropapillary Urothelial Carcinoma

PURPOSE OF REVIEW

This review will discuss micropapillary urothelial carcinoma with respect to biology, histopathologic characteristics, genetic and molecular features, diagnosis, clinical management, and future directions of research.

RECENT FINDINGS

Recent consensus opinion study showed only moderate interobserver reproducibility in the diagnostic criteria. The most reproducible criteria with the highest consensus were multiple nests in the same lacunar spaces. There are recent reports of high rates of intratumoral heterogeneity of ERBB2 amplification within tumor containing both micropapillary and classic urothelial components. Micropapillary urothelial carcinoma is a well-documented highly aggressive variant of urothelial carcinoma with proven worse outcomes. Accurate recognition and reporting of this pattern is critical for optimal management. Newer therapeutic strategies related to the molecular and genetic findings seen in MPUC remain to be explored further.

Non-invasive papillary urothelial carcinoma with 'micropapillary' architecture: clinicopathological study of 18 patients emphasising clinical outcomes

AIMS

Invasive micropapillary carcinoma is a recognised aggressive urothelial carcinoma variant. One prior study focusing on non-invasive (pTa) high-grade papillary urothelial carcinoma with micropapillary architecture has been reported.

METHODS AND RESULTS

We collected bladder transurethral resection specimens showing non-invasive high-grade papillary urothelial carcinoma with non-hierarchical secondary papillae lacking fibrovascular cores (i.e. micropapillary architecture). Cases with any invasive component or any prior history of invasive urothelial carcinoma were excluded. Twenty cases were identified from 16 male and two female patients (aged 55-86 years). Micropapillary architecture comprised from 10 to 95% (mean = 31%), but non-invasive cribriform (15 cases, comprising 5-60%, mean = 19%) and villoglandular patterns (nine cases, comprising 5-60%, mean = 24%) were commonly admixed. Treatment data were available for 16 patients: surveillance (n = 13), cystoprostatectomy (n = 1), BCG plus mitomycin (n = 1) and BCG (n = 1). Follow-up data were available from 16 patients (range = 1-128 months, mean = 50 months): 13 patients had no new occurrences to date (81%), two had stage progression to pT1 papillary urothelial carcinoma (13%) with one dying of other causes, and one died of other causes with no evidence of disease (6%).

CONCLUSION

Non-invasive urothelial carcinomas with micropapillary architecture are often admixed with non-invasive cribriform and villoglandular patterns. Stage progression to lamina propria invasion in only two of 16 patients (13%) is not higher than expected for otherwise typical pTa high-grade urothelial carcinomas and no progression to invasive micropapillary carcinoma was identified, adding further support to the current World Health Organisation recommendation excluding use of the term 'micropapillary' for pTa urothelial carcinoma.

Micropapillary urothelial carcinoma of urinary bladder displays immunophenotypic features of luminal and p53-like subtypes and is not a variant of adenocarcinoma

OBJECTIVES

Micropapillary urothelial carcinoma of the urinary bladder (MPUC) is a rare variant of urothelial carcinoma which has aggressive clinical characteristics. The objective is to investigate the molecular subtypes of MPUC and the impact to the clinical outcome and determine whether MPUC represents a variant of adenocarcinoma.

MATERIALS AND METHODS

We evaluated surrogate immunohistochemical markers of luminal, basal, and p53-like subtypes and correlated with prognosis and the expression of markers related to bladder adenocarcinoma and glandular differentiation in 56 cases of MPUC (10 cases of transurethral resection and 46 cases of radical cystectomy). Biomarker expression in co-existing conventional urothelial carcinoma was also analyzed. Cox regression analysis was performed to study the impact of molecular subtype on the clinical outcome.

RESULTS

Thirty-four cases (61%) met criteria for the luminal subtype. Twenty-two cases (39%) displayed a p53-like subtype. In contrast, 40/56 (71%) cases of coexisting conventional urothelial carcinoma were classified as luminal subtype and 16/56 (29%) cases were designated as p53-like subtype. There was no significant survival difference between luminal subtype and p53-like subtype. CDX2, villin, and cadherin 17 were negative in all cases. MUC1 was strongly and diffusely expressed in the stroma-facing surface of MPUC tumor cells in all the cases.

CONCLUSIONS

Our findings suggest that MPUC possesses characteristics of luminal and p53-like subtypes, and does not harbor phenotypic features of the basal subtype. There is no significant difference in the prognosis between luminal and p53-like subtype MPUC. MPUC is not a variant of adenocarcinoma and does not represent a form of glandular differentiation, in contrast to other organ sites.

Prognostic and therapeutic role of HER2 expression in micropapillary carcinoma of the bladder

Micropapillary carcinoma of the bladder (MPBC) is a variant type of infiltrating urothelial carcinoma, which portends a poor biological behavior in terms of disease stage at first diagnosis and clinical outcome; its peculiar morphology raises issues concerning the ability of tumor detection by imaging techniques and proper biopsy procedure, and the appropriate treatment for non-muscle infiltrating and muscle-infiltrating MPBC remains a matter of debate. On the basis of its established prognostic and therapeutic role in breast and gastro-esophageal cancer in the first instance, the human epidermal growth factor receptor-2 (HER2) has been investigated in selected case series of MPBC over the last 10 years. The aim of the present review was to summarize the existing evidence on HER2 status in MPBC, and to discuss its present and future utility in risk assessment and treatment choice of this uncommon, yet aggressive, disease.

Intratumoral heterogeneity of ERBB2 amplification and HER2 expression in micropapillary urothelial carcinoma

Micropapillary urothelial carcinoma (MPUC) is a rare but an aggressive variant of urothelial carcinoma. MPUC has been shown to commonly exhibit ERBB2 amplification and HER2 protein overexpression, but the frequency and distribution of these findings within micropapillary (MP) and not otherwise specified (NOS) components of tumors with mixed histology have not been addressed. Therefore, we evaluated ERBB2 amplification and HER2 expression in 43 MPUC cases by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). Of the 35 tumors containing both MP and NOS components, ERBB2 amplification was present in both the MP and NOS components of 12 tumors (34.3%), in only the MP component of 11 tumors (31.4%), and exclusively in the NOS component of 4 tumors (11.4%). HER2 protein overexpression was significantly more commonly present in the MP component compared to the NOS component within the same tumor (68.6% versus 34.3%, P = .012). Overall, there was a moderately positive correlation between HER2 protein expression and ERBB2 amplification in both MP (ρ = 0.59, P < .001) and NOS (ρ = 0.70, P < .001) components. All MP/NOS areas with IHC score 3+ and none of MP/NOS areas with IHC score 0 were associated with ERBB2 amplification. We conclude that ERBB2 amplification and HER2 overexpression are preferentially but not exclusively identified in the MP component compared to the NOS component within the same tumor. Our findings identify the presence of intratumoral heterogeneity of ERBB2 amplification and HER2 expression in MPUC and provide grounds for further investigation into the mechanisms underlying the development of MPUC.

Micropapillary Bladder Cancer: Insights from the National Cancer Database

Introduction: Micropapillary bladder cancer (MPBC) is a variant histology of urothelial carcinoma (UC) that is associated with poor outcomes however given its rarity, little is known outside of institutional reports. We sought to use a population-level cancer database to assess survival outcomes in patients treated with surgery, radiation therapy and/or chemotherapy.

Materials and Methods: The National Cancer Database (NCDB) was queried for all cases of MPBC and UC using International Classification of Disease-O-3 morphologic codes between 2004–2014. Primary outcome was survival outcomes stratified by treatment modality. Treatments included radical cystectomy (RC) with or without neoadjuvant chemotherapy (NAC) or adjuvant chemotherapy (AC).

Results: Overall 869 patients with MPBC and 389,603 patients with UC met the inclusion criteria. Median age of the MPBC cohort was 69.9 years (58.9–80.9) with the majority of the cohort presenting with high-grade (89.3%) and muscle invasive or locally advanced disease (47.6%). For cT1 MPBC, outcomes of RC and BPS were not statistically different. For≥cT2 disease, NAC showed a survival benefit compared with RC alone for UC but not for MPBC. On multivariable analysis, MPBC histology independently predicted worse increased risk of death. On subanalysis of the MPBC RC patients, NAC did not improve survival outcomes compared with RC alone.

Conclusions: Neoadjuvant chemotherapy utilization and early cystectomy did not show a survival benefit in patients with MPBC. This histology independently predicts decreased survival and prognosis is poor regardless of treatment modality. Further research should focus on developing better treatment options for this rare disease.

The Natural History, Treatment Pattern, and Outcomes of Patients With Micropapillary Bladder Carcinoma

OBJECTIVE

Micropapillary bladder carcinoma (MPBC) is a rare variant of urothelial cancer. Most literature on MPBC is from case series reports. This study's objective was to examine the epidemiology, natural history, and prognostic factors of MPBC using a population-based registry, in addition to a literature review.

METHODS

The Surveillance, Epidemiology, and End Results (SEER) database identified 98 histologically confirmed MPBC patients from 2001 and 2007. In addition, 213 MPBC cases were identified in published literature. The clinical, demographic characteristics, treatment, and survival outcomes were compared between these 2 cohorts.

RESULTS

Among patients identified in SEER, MPBC accounted for approximately 0.01% of primary bladder tumors, with the median age of 72 years (range, 26 to 95 y). Among the MPBC cases, 56.1% had muscle invasive disease, 75.5% had poor or undifferentiated histology, and 30.6% underwent a radical or partial cystectomy. The 1-, 3-, and 5-year overall survival rates for the SEER cohort were estimated at 84.5%, 57.3%, and 42.3%, respectively. Using multivariate analysis, tumor stage and marital status were the most significant predictors for cancer-specific survival. When comparing published single-institution studies to the SEER cohort, significant differences existed in demographic characteristics including age at diagnosis, male-to-female ratio, tumor stage, cystectomy treatment, and survival outcomes, likely reflecting differences in practice patterns.

CONCLUSIONS

This is the first population-based study to analyze MPBC's epidemiology, tumor characteristics, and survival rates. Emphases on early detection, cystectomy, and multimodality in treatment are needed.

Gene Expression Profile of the Clinically Aggressive Micropapillary Variant of Bladder Cancer

BACKGROUND

Progression of conventional urothelial carcinoma of the bladder to a tumor with unique microscopic features referred to as micropapillary carcinoma is coupled with aggressive clinical behavior signified by a high propensity for metastasis to regional lymph nodes and distant organs resulting in shorter survival.

OBJECTIVE

To analyze the expression profile of micropapillary cancer and define its molecular features relevant to clinical behavior.

DESIGN, SETTING, AND PARTICIPANTS

We retrospectively identified 43 patients with micropapillary bladder cancers and a reference set of 89 patients with conventional urothelial carcinomas and performed whole-genome expression messenger RNA profiling.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The tumors were segregated into distinct groups according to hierarchical clustering analyses. They were also classified according to luminal, p53-like, and basal categories using a previously described algorithm. We applied Ingenuity Pathway Analysis software (Qiagen, Redwood City, CA, USA) and gene set enrichment analysis for pathway analyses. Cox proportional hazards models and Kaplan-Meier methods were used to assess the relationship between survival and molecular subtypes. The expression profile of micropapillary cancer was validated for selected markers by immunohistochemistry on parallel tissue microarrays.

RESULTS AND LIMITATIONS

We show that the striking features of micropapillary cancer are downregulation of miR-296 and activation of chromatin-remodeling complex RUVBL1. In contrast to conventional urothelial carcinomas that based on their expression can be equally divided into luminal and basal subtypes, micropapillary cancer is almost exclusively luminal, displaying enrichment of active peroxisome proliferator-activated receptor γ and suppression of p63 target genes. As with conventional luminal urothelial carcinomas, a subset of micropapillary cancers exhibit activation of wild-type p53 downstream genes and represent the most aggressive molecular subtype of the disease with the shortest survival. The involvement of miR-296 and RUVBL1 in the development of micropapillary bladder cancer was identified by the analyses of correlative associations of genome expression profiles and requires mechanistic validation.

CONCLUSIONS

Micropapillary cancer evolves through the luminal pathway and is characterized by the activation of miR-296 and RUVBL1 target genes.

PATIENT SUMMARY

Our observations have important implications for prognosis and for possible future development of more effective therapies for micropapillary bladder cancer.

Micropapillary bladder cancer: current treatment patterns and review of the literature

OBJECTIVES

No guidelines exist for the management of micropapillary bladder cancer (MPBC) and most reports of this variant of urothelial carcinoma are case series comprising small numbers of patients. We sought to determine current practice patterns for MPBC using a survey sent to the Society of Urologic Oncology (SUO) and to present those results in the setting of a comprehensive review of the existing literature.

MATERIALS AND METHODS

A survey developed by the Translational Science Working Group of the Bladder Cancer Advocacy Network-sponsored Think Tank meeting was distributed to members of the SUO. The results from 118 respondents were analyzed and presented with a literature review.

RESULTS

Most survey respondents were urologists, with 80% considering bladder cancer their primary area of interest. Although 78% of the respondents reported a dedicated genitourinary pathologist at their institution, there were discrepant opinions on how a pathologic diagnosis of MPBC is determined as well as variability on the proportion of MPBC that is clinically significant. Among them, 78% treat MPBC differently than conventional urothelial carcinoma, with 81% reporting that they would treat cT1 MPBC with upfront radical cystectomy. However, the respondents had split opinions regarding the sensitivity of MPBC to cisplatin-based chemotherapy, which affected utilization of neoadjuvant chemotherapy in muscle-invasive disease.

CONCLUSIONS

The management of MPBC is diverse among members of the SUO. Although most favors early cystectomy for cT1 MPBC, there is no consensus on the use of neoadjuvant chemotherapy for muscle-invasive MPBC.

Clinical significance of micropapillary urothelial carcinoma of the upper urinary tract

BACKGROUND

The aim of this study was to improve understanding of the characteristics of micropapillary urothelial carcinoma (MPUC) in the renal pelvis and ureter, and to compare oncological outcomes between MPUC and non-MPUC.

METHODS

From September 1994 to October 2010, 418 patients underwent nephroureterectomy with bladder excision due to presumed urothelial carcinoma. Pathological review of all specimens was done by one uropathologist. Perioperative data from these patients were reviewed retrospectively. Patients were divided into MPUC and non-MPUC groups. Oncological outcomes were compared between the two groups via progression-free survival (PFS) and cancer-specific survival (CSS) rates.

RESULTS

A total of 386 patients were included in the study. Of these, seven patients (1.81%) had MPUC. The median follow-up duration was 39.0 months (IQR range 21.1-70.6). All MPUC patients were men and had lymphovascular invasion, and six patients (85.7%) had grade III and T3 disease. On univariable analysis, MPUC showed significantly worse prognosis with regard to disease progression (p<0.001). In the subgroup analysis confined to T3 or T4 disease, MPUC showed worse prognosis than non-MPUC in terms of PFS and CSS, respectively (p<0.05). In the multivariable model, MPUC still remained a statistically significant independent predictor for PFS (HR (95% CI)=3.85 (1.59-9.32), p=0.003). MPUC was associated with poorer CSS than non-MPUC (p<0.001).

CONCLUSIONS

We have observed that upper tract MPUC is associated with poor oncological outcomes in terms of PFS and CSS. MPUC was an independent prognostic factor for PFS in multivariable analysis.

Impact of micropapillary urothelial carcinoma variant histology on survival after radical cystectomy

OBJECTIVES

The role of micropapillary urothelial carcinoma (MUC) variant histology as an independent prognostic factor for survival after radical cystectomy has not been studied. Our aim was to examine the impact of MUC on survival.

MATERIALS AND METHODS

A retrospective analysis of prospectively collected data from the University of Southern California (USC) Bladder Cancer Database was performed. Between 1985 and 2008, 1,380 patients underwent radical cystectomy and superextended pelvic lymph node dissection for bladder cancer. All surgical specimens underwent central pathologic review by dedicated genitourinary pathologists. Histologic type was categorized as urothelial carcinoma (UC; n = 1,347) or MUC (n = 33). The outcomes were overall survival (OS) and recurrence-free survival (RFS). The Kaplan-Meier method and Cox proportional regression models were used to analyze survival data.

RESULTS

The median follow-up duration was 10 years (range, 0-25 years). Baseline characteristics were similar between histologic types except MUC was associated with advanced clinical (cTanyN1-3: 2% vs. 9%, P = 0.03) and pathologic (pTanyN1-3: 22% vs. 46%, P = 0.01) TNM stage, multifocality (38% vs. 58%, P = 0.02), and high nuclear grade (83% vs. 97%, P = 0.03). The predicted 5-year OS (61% and 67%, Log rank P = 0.96) and RFS (69% and 58%, Log rank P = 0.33) rates did not differ between patients with UC and MUC. Multivariable analysis showed that histologic type was not independently associated with OS (HR 0.91, 95% CI 0.55-1.49, P = 0.70) or RFS (HR 0.97, 95% CI 0.55-1.73, P = 0.92).

CONCLUSIONS

Outcomes of radical cystectomy for patients with MUC are similar to those with UC when controlling for other clinical and pathologic factors.

Noninvasive micropapillary urothelial carcinoma: a clinicopathologic study of 18 cases

Noninvasive micropapillary urothelial carcinoma consists of slender tufts of urothelial carcinoma lacking fibrovascular cores analogous to ovarian papillary serous tumors of borderline malignancy. Eighteen noninvasive micropapillary urothelial carcinoma cases were identified from the Pathology Department of The Johns Hopkins Hospital (2000-2011). Patients lacked history of invasive urothelial carcinoma. Two patterns of noninvasive micropapillary urothelial carcinoma were identified: (1) as a variant of noninvasive high-grade papillary urothelial carcinoma (high-grade papillary urothelial carcinoma/micropapillary urothelial carcinoma) (n = 13 cases) and (2) as a variant of urothelial carcinoma in situ (carcinoma in situ/micropapillary urothelial carcinoma) (n = 5 cases with 2 of these patients also having high-grade papillary urothelial carcinoma/micropapillary urothelial carcinoma). Of 18 patients, 16 (88%) were male with a mean age of 71.8 years (range, 54-87 years). Of the 12 patients initially treated with surveillance, Bacillus-Calmette Guérin, or intravesical chemotherapy, 4 did not recur and were without evidence of disease at 6, 21, 24, and 39 months. Four patients experienced recurrences with 3 of them without evidence of disease at 36, 52, and 72 months and with the fourth whose last follow-up was at 84 months when recurrence occurred. One patient is alive at 11 months with disease, and 1 died of other causes at 1 month. Two patients progressed to pT2 and pT3 disease at 5 and 21 months, respectively. It is critical to differentiate and clearly specify in pathology reports whether micropapillary urothelial carcinoma is invasive or noninvasive because invasive micropapillary urothelial carcinoma is an aggressive disease with a high degree of understaging, whereas some cases of noninvasive micropapillary urothelial carcinoma are not necessarily associated with an adverse outcome.

Lymphovascular Invasion in Micropapillary Urothelial Carcinoma: A Study of 22 Cases

Context.—Micropapillary urothelial carcinoma (MPUC) is a known aggressive variant of urothelial carcinoma. However, the reasons for its aggressiveness remain unclear.

Objective.—To investigate the frequency of lymphovascular invasion in 22 cases of MPUC.

Design.—Consecutive tissue sections were stained with D2-40 and CD34 to highlight lymphovascular channels associated with MPUC. Spaces containing tumor cells were scored as positive for lymphovascular invasion if the staining pattern on immunohistochemistry was distinct and circumferential.

Results.—Of 22 cases, 21 (95%) had lymphovascular invasion on immunohistochemical staining, with 91% lymphatic invasion and 4% vascular invasion. Interestingly, 8 cases were originally signed out as negative for lymphovascular invasion on the basis of hematoxylin-eosin–stained sections; of these, 7 (88%) had focal lymphovascular invasion evident on immunohistochemical staining.

Conclusions.—Our results confirm that micropapillary lacunae are not lymphovascular channels. However, nearly all MPUC tumors (95% in this series) have evidence of lymphovascular invasion by immunohistochemical analysis. Our data support the use of micropapillary features as a morphologic marker for lymphovascular invasion and MPUC as an adverse histologic type of urothelial carcinoma.

Micropapillary variant of urothelial carcinoma

Micropapillary carcinoma (MPC) of urinary tract is an uncommon variant of urothelial carcinoma with significant diagnostic and prognostic implications. Though MPC shows characteristic microscopic features, there exists interobserver variability and also it needs to be differentiated from the metastasis from other organs. The prognosis is generally poor, depending on the proportion of the micropapillary component in some reports. Early cystectomy in cases with only lamina propria invasion may be indicated according to recent studies. This review outlines the general features of this entity and briefly comments on the controversies and the recent development.