Squamous neoplasms of the prostate
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Squamous neoplasms of the prostate include squamous cell carcinomas and adenosquamous carcinomas of the prostate that account for two separate entities in the WHO classification of prostate tumors.
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Squamous cell carcinomas of the prostate are very rare and encompass <1% of prostate cancers and adenosquamous carcinomas are even less frequent 1-6.
Squamous cell neoplasms in particular adenosquamous carcinoma are associated with the following conditions 1-7:
- prostatic schistosomiasis
- acinar adenocarcinoma on androgen deprivation therapy
- radiation therapy
The diagnosis of prostatic squamous cell neoplasms is based on typical histological features.
Typical symptoms include voiding symptoms such as irritation, dysuria or obstructive symptoms 1. Pure squamous cell carcinomas do not feature a relevant elevation in prostate-specific antigen (PSA) 2-5, whereas adenosquamous carcinoma might present with slight elevation.
Squamous cell carcinomas tend to cause osteolytic bone metastases more often than osteoblastic metastases 1-6.
Proposed diagnostic criteria for prostatic squamous cell carcinomas include 2,3:
- clear features of malignancy
- definite squamous differentiation
- no squamous cell carcinoma elsewhere
- lack or of glandular carcinoma component (otherwise it would be adenosquamous)
- no previous androgen deprivation therapy
Adenosquamous carcinoma is characterized by both a glandular or often high-grade adenocarcinoma component and squamous cell carcinoma components of varying degrees 1,4,6.
Squamous cell carcinomas and components are not assigned a Gleason grade but can be applied to a three-tiered grading scheme 6. In the case of adenosquamous carcinomas, it was suggested that the Gleason grade could be used for glandular components in absence of androgen deprivation therapy 6.
The etiology of squamous cell carcinoma of the prostate is not fully understood 5.
Squamous cell carcinomas can arise from the periurethral glands the prostatic acini or the basal cell lining 1.
Grossly tumors have been described as solid firm masses measuring up to 6.5 cm with whitish-yellow to tannish-grey appearance and central extension with compression of the prostatic urethra 6.
Microscopically prostatic squamous cell carcinomas are characterized by the following histological features 1,4,6:
- infiltrative sheets and nests of polygonal cells with nuclear atypia
- cellular keratinization or keratin pearl formation
- intercellular bridges
- irregular growth and cellular aplasia
Adenosquamous carcinomas have been described to show either transition to or distinct glandular components 6.
Immunohistochemistry stains usually express p53 8 and cytokeratin 34βE12. Squamous tumor cells are typically negative for prostatic markers as the prostate-specific antigen (PSA) or prostatic acid phosphatase (PAP) or P501S 1,2. AMACR might be positive in adenosquamous carcinoma.
Prostate and/or pelvic imaging might reveal a prostatic mass and/or pelvic lymphadenopathy subject of tumor extent and stage 3.
Since prostatic squamous cell carcinoma requires exclusion of squamous carcinoma elsewhere imaging for a full staging is required to exclude secondary tumor involvement of the prostate.
On transrectal ultrasound, lesions have been described as hypoechoic 4.
MRI of the prostate has been described to show an infiltrative but otherwise uncharacteristic mass in a few cases reports 3-5 with possible extraprostatic extension, seminal vesicle or bladder neck invasion depending on the extent and stage of the tumor.
- T2: hypointense
- DWI: diffusion restriction (hyperintense on high b-value and hypointense on ADC map)
- DCE (Gd): focal early enhancement
PET-CT might show FDG-uptake in the primary tumor regional lymph nodes and/or distant metastases 3,6.
The radiological report should include a description of the following:
- form, location and size
- tumor margins
- extraprostatic extension
- seminal vesicle invasion
- bladder neck invasion
- suspicious or enlarged lymph nodes
Treatment and prognosis
The prognosis of squamous cell carcinomas and adenosquamous carcinomas of the prostate is poor with mean survival times ranging between 6 months and 2 years 1-3,6. Management strategy is usually multimodal and includes surgery as well as adjuvant radiotherapy and chemotherapy 3.
Conditions mimicking the clinical presentation or imaging appearance of prostatic urothelial carcinoma include 1,2:
- prostatic adenocarcinoma
- squamous metaplasia after androgen deprivation therapy
- urothelial carcinoma of the prostate
- other squamous cell carcinomas with prostatic involvement
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