Verrucous Squamous Hyperplasia of the Urinary Bladder: A Series of 23 Cases

The Surgical Pathology Database of The Johns Hopkins Medical Institute's division of surgical pathology and the case files of the senior author (J.I.E.) were searched for cases of “verrucous squamous hyperplasia” or “verrucous hyperplasia” of the urinary bladder from August 2010 to February 2021. Cases were separated into those with and without concurrent cancer, and all avenues were exhausted to obtain clinical information. For all patients, blocks or unstained slides were sought, and human papillomavirus (HPV) in situ hybridizations were performed for high-risk HPV (HPV 16/18/26/31/33/35/39/45/51/52/53/55/56/58/59/66/68/73/82) in available cases. In cases with cancer, HPV in situ hybridization was performed on the invasive component. HPV in situ hybridization was performed using the fresh formalin-fixed, paraffin-embedded 2.5 HD detection kit (Brown; DS9790, Leica). In brief, formalin-fixed, paraffin-embedded tissue was sectioned at 4-μm increments, deparaffinized, heated, treated with a protease and hydrogen peroxide, and hybridized with a probe at 40°C for 2 hours plus Amp1 to Amp6. After washing and amplification, target RNA was stained with 3,3′-diaminobenzidine. Counterstaining was performed with hematoxylin and bluing agent, and positive control staining was indicated by brown punctate cytoplasmic dots. For cases with available material, p53 (Roche Diagnostics, Basel, Switzerland) immunohistochemistry was performed.

A total of 23 cases of verrucous squamous hyperplasia of the urinary bladder were identified (Figure 1, A). All 23 were consults sent to the senior author. Of the 23 cases, 11 (47.8%) had concurrent in situ or invasive carcinoma (range, 31–88 years; median, 72 years), whereas 12 (52.2%) lacked concurrent carcinoma (range, 41–96 years; median, 71 years). The male to female ratio for all cases was 1.3:1 (1.2:1 for cases with carcinoma and 1.4:1 for cases with verrucous squamous hyperplasia only).

Of the 12 cases (52.2%) without concurrent carcinoma, clinical follow-up was available for 7 (58.3%; Table 1). One patient (8.3%) had clinical features highly suggestive of carcinoma and was scheduled for cystectomy but canceled surgery and was subsequently lost to follow-up. One patient each (8.3%) had fungal cystitis and developed a benign ulcer. A total of 4 of 7 patients (57.1%) were dead not from disease, but no further follow-up was available. Clinical history preceding diagnostic biopsy was available for 10 of 12 patients (83.3%). A total of 3 of 10 patients (30%) had a prior or concurrent history of chronic urinary tract infections, 3 of 10 (30%) with prior instrumentation, 2 of 10 (20%) with Schistosoma haematobium infection, 2 of 10 (20%) with prior radiation therapy, 2 of 10 (20%) with prior or concurrent history of stones, and 1 of 10 (10%) each with prior history of chemotherapy, prior history of bladder cancer, keratinizing squamous metaplasia, follicular cystitis, incontinence, and diverticulum.

Of 11 patients with concurrent carcinoma, 4 (36.4%) had extensive verrucous squamous hyperplasia with at least squamous cell CIS/cannot rule out superficial invasion (Figures 1 and 2). Two patients (18.2%) had mixed sarcomatoid urothelial carcinoma with squamous cell carcinoma in separately submitted parts. Two patients (18.2%) had invasive, well-differentiated squamous cell carcinoma (Figure 1, B through D), 1 (9.1%) of whom had long-standing schistosomiasis. One patient (9.1%) had invasive poorly differentiated squamous cell carcinoma. One patient (9.1%) had invasive high-grade squamous cell carcinoma with a prominent associated lymphocytic infiltrate (Figure 2). In another biopsy from a separate location, this patient also had concurrent invasive high-grade urothelial carcinoma with squamous differentiation. One patient (9.1%) had urothelial CIS, cannot exclude invasion. In 4 patients (36.4%) with available clinical follow-up, 3 (75%) were dead from disease (6–24 months), and 1 (25%) was alive without evidence of disease (42 months; Table 2). In 4 patients (36.4%) with available clinical history, 1 (25%) had prior bladder cancer history, 1 (25%) had a long-standing history of neurogenic bladder, 1 (25%) had latent exposure to S haematobium, and 1 (25%) had bladder stones and diverticulum, with the former 2 (50%) both dead of disease (Table 2).

HPV was negative in all cases tested, including 6 cases with carcinoma and 7 cases with only verrucous squamous hyperplasia. The 3 cases tested for immunohistochemical expression of p53 (all verrucous squamous hyperplasia–only cases) demonstrated normal/wild-type staining in both the basilar layer and suprabasilar regions. Thus, none showed a mutant-type pattern (ie, diffuse expression or complete loss of staining [“null” pattern]).

Verrucous squamous hyperplasia is a rare squamous lesion found in the bladder. It is composed of acanthosis with spiky church spire–like squamous hyperplasia with hyperkeratosis and parakeratosis (Figure 1, A). In the head and neck, it is considered an irreversible precursor to malignancy.^7,8  In the larynx, verrucous squamous hyperplasia has a higher risk of progression to squamous cell carcinoma than other forms of intraepithelial neoplasia and may contain a range of cytologic atypia or may lack cytologic atypia entirely.^8–10  In the oral cavity, where these lesions are synonymously termed proliferative leukoplakia or verrucous hyperplasia, 29% of verrucous squamous hyperplasia cases contain verrucous carcinoma, 10% to 37% contain concurrent squamous cell carcinoma, and 29% to 66% contain dysplasia.^8,10  In the study by Silverman and Gorsky,¹¹  70% of patients with “verrucous leukoplakia” developed squamous cell carcinoma with a mean follow-up of 7.7 years. The influence of HPV in this site remains controversial, with reported rates of HPV positivity between 0% and 25%.^12–15 

There is a paucity of literature on verrucous squamous hyperplasia of the urinary bladder. In 2006, Guo et al²  from our institution performed a clinicopathologic study on noninvasive squamous lesions of the urinary bladder, including 5 patients with verrucous squamous hyperplasia. Of these 5 patients, 1 (20%) developed squamous cell carcinoma, 1 (20%) developed squamous cell CIS, 1 (20%) had persistent verrucous squamous hyperplasia, and 2 (40%) had no evidence of disease. Subsequently in 2007, Lagwinski et al⁶  looked at clinicopathologic characteristics and outcome data for patients with squamous cell carcinoma who underwent partial or radical cystectomy. At that time, they noted several associated squamous lesions in the cohort of 45 patients, including verrucous squamous hyperplasia in 3 (6.7%). In the current series, we demonstrate that roughly half (11 of 23; 47.8%) of patients with verrucous squamous hyperplasia of the bladder had concurrent invasive or in situ carcinoma, demonstrating predominant or pure squamous differentiation in most cases. We were unable to ascertain the progression risk for patients without concurrent invasive cancer because of a lack of robust follow-up and a limited number of patients. However, of 7 patients with clinical follow-up, at least 1 (14.3%) was recommended to undergo radical cystectomy for clinically evident carcinoma, which presented as diffuse carpeting of the bladder on cystoscopy. At a minimum this suggests that verrucous squamous hyperplasia remains a high-risk association for squamous cell carcinoma or squamous cell CIS and that patients with isolated verrucous squamous hyperplasia should be followed closely clinically. Although we cannot make definitive conclusions on the underlying etiology of verrucous squamous hyperplasia because of the small sample size of our study, 9 of 10 patients (90%) had chronic inflammatory conditions or were exposed to a significant insult that would necessitate prolonged regeneration and repair of urothelial mucosa. At least in part, this association seems similar to the current understanding of the pathogenesis of usual keratinizing squamous metaplasia of the bladder.

Although some may thus view this lesion simply as a variant of keratinizing squamous metaplasia, we believe that until further investigation is undertaken it should be documented distinctly for several reasons. First, although we do not have robust cystoscopic history, 2 of our cases presented with diffuse carpeting of the bladder, and it may be that there is a distinct cystoscopic impression that differs from that of keratinizing squamous metaplasia. In the bladder, where careful clinical-pathologic correlation is critical, delineating a verruciform lesion from a flat lesion is of value, even if one is a variant of the other. Second, we do not, at the present time, have enough data on either high-risk associations or progression risk to conclude that it is not a distinct variant worth specifically mentioning. Third, although there is a substantial amount written about keratinizing squamous metaplasia, very little is written about verrucous squamous hyperplasia. We believe that it is important to document verrucous squamous hyperplasia in order to increase its recognition by pathologists to facilitate future investigation. Fourth and finally, the differential diagnosis between the 2 entities is different because keratinizing squamous metaplasia is a flat lesion, whereas verrucous squamous hyperplasia is a verruciform one.

Some of the verrucous squamous hyperplasia cases without carcinoma in this series have features that overlap with and resemble precursor lesions described in the vulva. Vulvar squamous cell carcinoma and its precursors are subdivided into HPV-dependent and HPV-unrelated types. The latter consist of those that are TP53 mutation-related and TP53 mutation-independent.¹⁶  The TP53 mutation–related precursor lesions include differentiated vulvar intraepithelial neoplasia, which usually lacks verrucous architecture but displays basilar atypia and suprabasilar abnormal keratinocyte maturation.¹⁷  In contrast, the TP53 mutation-independent putative precursors include VAAD³  and DEVIL.^4,5  Also, it has been suggested that VAAD and DEVIL represent the same lesion.^4,16  VAAD/DEVIL is histologically characterized by verruciform acanthosis, multilayered parakeratosis, loss of the granular cell layer, cytoplasmic pallor in the upper layers of the squamous epithelium, and bland nuclei, including a lack of basilar atypia. In addition to an absence of TP53 mutations, VAAD/DEVIL has been shown to be associated with PIK3CA, ARID2, and HRAS mutations.^4,5  Furthermore, it has been proposed that VAAD/DEVIL is a precursor of verrucous carcinoma. Although molecular analysis of PIK3CA, ARID2, and HRAS was not the aim of this study, the combined histologic features and lack of mutant-type immunohistochemical expression of p53 may suggest that a subset of verrucous squamous hyperplasias of the urinary bladder are analogous to the HPV-unrelated/TP53 mutation-independent precursor lesions of the vulva (ie, VAAD/DEVIL); however, definitive conclusions with the limited number of cases tested are not possible.

Other considerations in the histologic differential diagnosis of verrucous squamous hyperplasia of the urinary bladder primarily include keratinizing squamous metaplasia, papillary urothelial carcinoma with squamous differentiation, verrucous carcinoma, squamous cell carcinoma in situ, CIS with squamous differentiation, and rarely, secondary involvement by a gynecologic (namely ectocervical) primary. In contrast to verrucous squamous hyperplasia, keratinizing squamous metaplasia shows flat compact hyperkeratosis without the verruciform, undulating, and almost papillary at times silhouette of verrucous squamous hyperplasia observed on low magnification. The morphologic similarity between verrucous carcinoma and verrucous squamous hyperplasia is that they both share the same surface histology as cytologically benign keratinizing squamous epithelium. Whereas verrucous squamous hyperplasia is a noninvasive diagnosis, the presence of an irregular pushing border into the lamina propria distinguishes verrucous carcinoma from verrucous squamous hyperplasia. The distinction may be challenging on superficial biopsy and requires evaluation of the base of the lesion to assess for invasion. In CIS with squamous differentiation, typically there are other areas with more usual CIS, compact hyperkeratosis is either absent or focal, and the verruciform silhouette is absent. In papillary urothelial carcinoma with squamous differentiation, the degree of cytologic atypia exceeds that identified in verrucous squamous hyperplasia without dysplasia, and usual urothelium can be identified, if only focally. On rare occasions, a gynecologic origin may be considered in the differential diagnosis with verrucous squamous hyperplasia. In this setting, both p16 and GATA-binding protein 3 (GATA-3) represent potential pitfalls because both lesions may be positive¹⁸  and should not be used. HPV in situ hybridization can be invaluable, however, because it is positive in most gynecologic squamous cancers of cervical origin and negative in the vast majority of urothelial squamous lesions.

A weakness in our study is the small number of cases and the limited clinical follow-up. However, these cases are exceptionally rare and may be underappreciated. Because all avenues to obtain clinical follow-up were exhausted, we felt it was best to provide pathologists and treating clinicians with as much current information as possible in order to improve recognition of the entity for subsequent investigation. In conclusion, our data support that verrucous squamous hyperplasia of the bladder is unrelated to HPV infection and frequently associated with invasive carcinoma, most frequently squamous cell carcinoma. In cases unassociated with carcinoma, progression risk is unclear given the limited number of cases with adequate follow-up but appears to be associated with chronic inflammatory conditions. Until more is known about the entity and in light of its strong association with carcinoma, we recommend close clinical follow-up in patients with a diagnosis of verrucous squamous hyperplasia.