Semiquantitative immunohistochemical (IHC) pixelwise H-score of mitochondrial transcription factor A (TFAM) in gastric adenocarcinoma (GAC): clinicopathological significance and association with p53 and HER2

Background: The roles of p53 and HER2 in gastric adenocarcinoma (GAC) have been extensively studied; nevertheless, the contribution of mitochondrial transcription factor A (TFAM) remains unclear. Concerning TFAM’s pivotal role in mitochondrial biogenesis, this study aimed to evaluate the TFAM expression in GAC and to assess its associations with p53 and HER2 expressions and clinicopathological outcomes. Methods: We retrospectively analyzed 77 GAC patients who underwent upfront gastrectomy at Taipei Hospital between 2012 and 2021. Their clinicopathological profiles were recorded in detail. Immunohistochemical (IHC) staining for TFAM, p53, and HER2 protein expressions was semiquantified using IHC pixelwise H-score analyzed by ImageJ plugins IHC profiler. Associations between two continuous variables were assessed by Spearman’s correlation coefficient (CC), and trendlines were fitted using SPSS’s curve estimation function. The optimal cutoff for survival discrimination was derived from receiver operating characteristic (ROC) curve analysis by selecting the threshold with the highest Youden index and area under the curve (AUC). Prognostic variables with a Log-rank test p-value ≤ 0.1 were entered into a multi-variate Cox proportional hazards regression (Cox regression) model to identify independent ones and their relative hazards ratio (HR). Results: TFAM IHC pixelwise H-score was significantly associated with advanced T and N status, lymphovascular invasion, perineural invasion and poor differentiation (all’s p < 0.05), and was inversely correlated with tumor size (Spearman’s rho CC = -0.402, p < 0.001) in a logarithmic distribution (p < 0.001). A positive correlation (Spearman’s rho CC = 0.312, p = 0.006) in cubic distribution (p < 0.001) was observed between p53and TFAM IHC pixelwise H-scores. ROC analysis yielded a TFAM IHC pixelwise H-score cutoff of 43.0 (AUC = 0.650, 95%CI = 0.515–0.785, p = 0.047; sensitivity = 0.490, specificity = 0.810) to dichotomize high and low groups. In multi-variate Cox regression, low TFAM IHC pixelwise H-score (HR = 2.332, 95%CI = 1.136–4.787, p = 0.021), M1 status (HR = 3.582, 95%CI = 1.608–7.979, p = 0.002), and perineural invasion (HR = 4.506, 95%CI = 1.541–13.177, p = 0.006) were identified as independent variables to poor prognosis with elevated HRs. Among patients with high TFAM expression, higher HER2 IHC pixelwise H-score was associated with elevated hazard (HR = 1.010, 95%CI = 1.002–1.019, p = 0.020, Cox regression, uni-variate). Among M1 patients, higher p53 IHC pixelwise H-score was related to elevated hazard (HR = 1.029, 95%CI = 1.004–1.056, p = 0.025, Cox regression, uni-variate). Conclusions: ROC and multi-variate Cox regression identified low TFAM expression as an independent poor prognostic variable for operable GAC patients, implying its potential as a quantitative prognostic biomarker. The observed associations with p53 and HER2 are hypothesis-generating and they require further validation to clarify TFAM’s role in Warburg effect and GAC progression.