Here we studied LMP-1 expression, and histopathological characteristics of the EBV-positive and -negative PCa tissues, followed by survival analysis of the patients from the two groups
Descriptive and association analysis showed that the mean major and total Gleason scores in EBV-positive PCa samples were higher as compared to EBV-negative PCa samples, and a positive association between Gleason scores (total). This finding suggests an association between EBV infection in the prostate cancer tissues and the higher total Gleason scores. This observation was corroborated by an analysis of PNI distribution, where a higher percentage of EBV-positive PCa (80%) had PNI as compared to EBV-negative PCa samples (67.3%), and EBV status was positively correlated with PNI, further strengthening the possibility that EBV infection might be associated with the aggressive forms of cancer. These findings are clinically important as Gleason score and PNI are associated with an aggressive form of PCa (18–21). Although in literature, nothing is known about EBV and its relationship with PCa, however, it has been reported that the presence of EBV in nasopharyngeal carcinoma is associated with the progression of cancer since it involves multiple hallmarks of cancer (22, 23). Clinically, EBV-positive nasopharyngeal carcinoma tends to be more invasive with increased metastasis as compared with EBV-negative nasopharyngeal carcinoma cases (24). At the same time, EBV-positive nasopharyngeal carcinoma cases are more responsive to radiotherapy and chemotherapy (25) as compared to EBV-negative NPC cases.
Next, LMP1 expression was determined in PCa samples. Although, for EBV detection, an RNA in situ hybridization (ISH) is the test of the choice (26), however, IHC-based detection of LMP1 is commonly performed especially in low and middle-income countries (27, 28). Some studies have reported that the rates of detection between IHC LMP and ISH are comparable (29, 30). We found LMP1 expression in 70.96% of the cases. To the best of our knowledge, IHC-based expression of EBV LMP1 in PCa tissues has been reported for the first time in this study. Among EBV-associated epithelial cancers, the IHC-based expression of EBV LMP1 is better characterized in EBV-associated nasopharyngeal carcinoma and has been observed in variable percentages in different studies, ranging from 40–86% (27, 31–35).
In this report, we have found higher percentage of intratumoral lymphocytic infiltration, tumor stromal lymphocytic infiltration and the lymphocytic infiltration in the benign tissue adjacent to the tumor tissue in EBV-positive PC samples as compared to EBV-negative PCa samples. These findings seem to support earlier reported studies where EBV-positive nasopharyngeal carcinoma samples had a significantly higher number of tumor-infiltrating lymphocytes as compared with EBV-negative nasopharyngeal carcinoma samples (36), and the presence of a higher number of tumor-infiltrating lymphocytes is associated with better survival (37). Similarly, better survival is associated with the presence of tumor-infiltrating lymphocytes in EBV-associated gastric carcinoma (38). Tumor-infiltrating lymphocytes have an important role in prostate carcinoma (39), however, further studies are required to establish the role of EBV-associated tumor-infiltrating lymphocytes in prostate carcinoma.
Lastly, a survival benefit analysis in EBV-positive and EBV-negative patients with PCa was performed. Overall, the EBV status was independent of survival proportions, however, a survival advantage was observed in the 38th month, where the EBV-positive PCa group was found to have a higher survival as compared to the EBV-negative group. Previous studies have suggested a conflicting role of EBV in cancer; Song et al showed that the presence of EBV conferred a survival advantage to the patients with EBV-associated gastric carcinoma (40), whereas in EBV-associated nonkeratinizing subtype of nasopharyngeal carcinoma, EBV infection has been associated with increased risk of distant metastasis (41, 42). The role of EBV in the progression of prostate carcinoma has not been previously reported. As indicated earlier, the enhanced survival may be attributed to increased lymphocytic infiltration, as is observed in EBV-associated nasopharyngeal and gastric carcinoma (37, 38). There are certain limitations with respect to the survival analysis. Firstly, other clinical parameters, such as treatment regimens during the period of this analysis could not be included as this information was not available for biopsies. Secondly, there was an imbalance in the number of EBV-positive (n = 25) and EBV-negative retrospectively collected PCa samples (n = 49), which might introduce some sampling bias (43). However, this bias may be limited as events (deaths) were considered and not the actual sample number in the analysis. Finally, the survival analysis was limited to 38 months (the current month) only. Analysis beyond 38 months may provide additional information on survival benefits.
In conclusion, this study provides evidence that the presence of EBV in the prostate carcinoma tissues may lead to aggressive forms of PCa. Further studies with a larger sample size are required to strengthen the link between EBV, PCa prognosis, and survival.