Immunohistochemical Features of Prostatic Carcinoma in Southwest Nigeria: A Ten-Year Retrospective Study

Background: The diagnosis of prostatic adenocarcinoma relies on a constellation of architectural and cytological features. However, some cases may pose some diagnostic challenges especially where there are only small foci of cancer where only a few atypical glands are present, especially in needle biopsies. Therefore, immunohistochemistry may be used to differentiate benign from malignant proliferations, primary prostatic lesions and secondary lesions from other sources.

Objectives: To determine the immunohistochemical profile of prostatic carcinoma seen at the Department of Morbid Anatomy and Histopathology, Ladoke Akintola University of Technology Teaching Hospital, Osogbo, using high molecular weight cytokeratin, alpha-methylacyl co-enzyme A racemase and Ki-67 markers.

Methods: This was a retrospective study involving all cases of diagnosed prostatic carcinoma in the Department of Morbid Anatomy and Histopathology of the Ladoke Akintola University of Technology Teaching Hospital, Osogbo, Osun State, Nigeria. The histologic slides were reviewed for the histological variant of prostatic carcinoma as well as the Gleason histologic grade of the tumour and the presence of high-grade prostatic intraepithelial neoplasia (HGPIN). Immunohistochemistry was done using high molecular weight Cytokeratin (HMWCK), a basal cell marker, and alpha-methyl acyl CoA racemase (AMACR), a marker of malignant prostatic cells. Ki-67 antibody was used to assess the proliferating index of the tumour.

Results: The majority of cases (72.8%) were seen between the ages of 61 and 80 years while the peak age of frequency was the 71-80-year age group. Prostatic carcinoma constituted 4.4% of all tumours and 18.7 % of malignant tumours. A total of 204 (54.8%) cases were well-differentiated tumours, 104 (27.9%) moderately differentiated, and 64 (17.2%) were poorly differentiated. The most common histologic type (73.7%) was acinar adenocarcinoma, while colloid carcinoma was the least common variant (0.2%). HGPIN was seen in 111 cases (29.9%). Most of the cases of prostatic carcinoma (78.8%) were negative for Ki-67. All well-differentiated tumours were negative for the marker.

Conclusion: Prostatic carcinoma is the commonest malignant tumour in males in this environment with a frequency that increases with age. Poorly differentiated tumours are more like to be associated with a younger age at presentation. HGPIN appears to be a true precursor lesion. Immunohistochemistry with HMWCK and AMACR should be reserved for equivocal cases only. The Ki-67 marker may help segregate tumours with poorer prognosis.