A 72-year-old man is diagnosed with metastatic prostate cancer on staging investigations. Histology confirms adenocarcinoma. Which is the most common histological type of prostate cancer?

Explanation

## Most Common Histological Type of Prostate Cancer **Key Point:** Adenocarcinoma accounts for >95% of all prostate cancers. Within adenocarcinoma, the **acinar (glandular) type** is by far the most common subtype, representing approximately 90–95% of all prostate adenocarcinomas. ### Histological Classification of Prostate Cancer | Histological Type | Frequency | 5-Year Survival | Key Features | | --- | --- | --- | --- | | Acinar adenocarcinoma | ~95% | 65–85% (stage-dependent) | Most common; arises from glandular epithelium | | Small cell carcinoma | <1% | <5% | Neuroendocrine; highly aggressive | | Squamous cell carcinoma | <1% | <5% | Rare; very poor prognosis | | Transitional cell carcinoma | <1% | Variable | Arises from urothelium; rare | | Mucinous adenocarcinoma | <1% | Poor | Produces mucin; uncommon | ### Acinar Adenocarcinoma: Subtypes and Variants Within acinar adenocarcinoma, several morphological variants exist: 1. **Conventional acinar type** — most common; well to moderately differentiated glands. 2. **Cribriform pattern** — intermediate differentiation; associated with higher Gleason scores. 3. **Ductal adenocarcinoma** — more aggressive; higher grade. 4. **Mucinous (colloid) adenocarcinoma** — rare; mucin-producing. 5. **Signet-ring cell adenocarcinoma** — very rare; poor prognosis. **High-Yield:** The **Gleason grading system** is used to stratify acinar adenocarcinomas: - Gleason score = primary pattern + secondary pattern (range 2–10). - Score ≥8 indicates high-grade disease with poor prognosis. - Score 6 or less indicates low-grade disease with better prognosis. ### Why Acinar Adenocarcinoma? Prostate cancer arises from the **glandular epithelium** of the prostate, specifically from the acini and ducts. The acinar cells are the primary secretory units, making them the most common site of malignant transformation. Adenocarcinoma is the natural consequence of epithelial malignancy in a glandular organ. **Clinical Pearl:** Neuroendocrine differentiation (small cell carcinoma) can occur as a secondary phenomenon in advanced prostate cancer, particularly after androgen deprivation therapy, but it is not the primary histology at diagnosis. **Mnemonic:** **CAST** — Common Adenocarcinoma Subtypes in prostate: - **C**ribriform - **A**cinar (conventional) - **S**ignet-ring (rare) - **T**ubular [cite:Robbins 10e Ch 21]