Large cell neuroendocrine carcinomas (LCNEC) of the prostate or prostatic large cell neuroendocrine carcinomas are very aggressive and rare high-grade neuroendocrine tumors that are usually observed in the presence of an already existing adenocarcinoma and very rarely found alone.
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Epidemiology
Large cell neuroendocrine carcinomas of the prostate are extremely rare, particularly if they occur alone 1-3. The largest case series comprised only 7 cases, and cases of pure large cell neuroendocrine tumors are very scarce 3,4.
Associations
Large cell neuroendocrine carcinomas of the prostate often occur in the presence of existing acinar adenocarcinomas in patients on long-term androgen deprivation therapy (ADT) 1-3.
Diagnosis
The diagnosis of prostatic large cell neuroendocrine carcinomas is based on histological features and immunohistochemistry.
Clinical presentation
Given the tumor volume, the prostate-specific antigen (PSA) might be elevated but is often low. Voiding difficulties, urinary retention, hematuria, or metastases are other presenting symptoms 4. Due to the close connection with acinar adenocarcinoma, there might be a known history of prostate cancer.
Pathology
Large cell neuroendocrine carcinomas are high-grade neoplasms of the prostate which resemble pulmonary large cell neuroendocrine carcinomas 5, occur alone only very rarely but are usually associated with an acinar adenocarcinoma of the prostate 1,2.
Etiology
The etiology of prostatic large cell neuroendocrine carcinomas is unknown.
Macroscopic appearance
Macroscopically prostatic large cell neuroendocrine carcinomas are usually characterized by large tumors nodules at the time of diagnosis.
Microscopic appearance
Histologically prostatic large cell neuroendocrine carcinomas are characterized by the following morphological features 1-5:
tumor cells with abundant cytoplasm
coarse nuclei with prominent nucleoli
vesicular clumped or coarse salt and pepper chromatin
sheet and cord-like growth patterns with large nests
lack of glandular formation
peripheral palisading architecture
geographic necrosis and apoptosis
high mitotic count
low nuclear to cytoplasmic ratio
Immunophenotype
Immunohistochemistry stains are usually positive for at least one neuroendocrine marker as synaptophysin, CD56 or chromogranin A. It is usually only focally positive or negative for prostate-specific antigen (PSA) 1-5.
Besides large cells, neuroendocrine carcinomas are usually characterized by a Ki67 index >50% 1,2. Other potentially positive expressions include CD57 P504S and PSMA 2,3.
Radiographic features
Large cell neuroendocrine carcinomas of the prostate are very rare and are mostly seen in close association with acinar adenocarcinoma of which the radiographic features are well described.
They might be already large at the time of diagnosis and there might be pelvic lymph node metastases 4.
MRI
Due to their very rare occurrence, there is a paucity of radiological descriptions of large cell neuroendocrine carcinomas of the prostate.
Nuclear medicine
There are case descriptions of large cell neuroendocrine tumors showing uptake of FDG, PSMA and/or somatostatin receptor positivity 7.
Radiology report
The radiological report should include a description of the following features 4:
form, location and size
tumor margins
extraprostatic extension
seminal vesicle invasion
bladder or rectal invasion
suspicious or enlarged lymph nodes
Treatment and prognosis
The prognosis of large cell neuroendocrine carcinoma of the prostate is very poor with descriptions of mean survival rates of about 7 months. This is probably because the tumor is very aggressive and often advanced at the time of diagnosis on one hand and secondary to a limited treatment experience on the other 2. Therefore management will be very likely multimodal 4. Besides, unlike small cell carcinoma of the prostate, reports exist that pure forms of prostatic large cell neuroendocrine carcinoma responded to androgen deprivation therapy 3-5.
Differential diagnosis
Conditions and tumors that can mimic the clinical presentation or imaging appearance of prostatic large cell neuroendocrine carcinoma include 1-6:
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