Expression of phospho-ERK1/2 and PI3-K in benign and malignant gallbladder lesions and its clinical and pathological correlations

108 gallbladder carcinoma specimens were collected from the First and Second Xiangya hospitals affiliated to Central South University, and People's Hospital of Hunan Province, Changsha, China. 77 (71.3%) specimens came from female patients and 31 males (28.7%). All specimens were diagnosed as adenocarcinomas, of which 9 had adenoma lesions, 29 were highly differentiated, 29 moderately differentiated, 30 poorly differentiated, and the remaining 11 were mucous adenomas (10.2%). During surgery, 59 cases (54.6%) were found to have invasion of peri-cholecystic tissues and organs, 59 cases (54.6%) demonstrated local lymph node metastases; and 58 cases (53.7%) had evidence of gallstones/cholelithiasis. The applied surgical modalities include radical resection in 34 cases (31.5%), palliative resection/operation in 48 cases (44.4%), and 26 cases (24.1%) unresectable due to local invasion into critical structures or metastasis beyond regional confines. From the above 108 gallbladder adenocarcinoma samples, we obtained the peri-tumor tissues from 46 case (distance to adenocarcinomas ≥3 mm), 10 of which were normal by pathological analysis. Mild, moderate or severe atypical proliferation was observed in 10, 12 and 14 cases, respectively. 15 specimens of gallbladder adenoma polyps were obtained from the Second Affiliated Hospital of Central South University (including 10 female and 5 male, average age 52 years old, range 42 to 60 years). The polyploidy adenomas ranged from 0.08 – 15 mm in size, 5 out of the 15 had moderate to severe proliferation. In addition, 35 chronic cholecystitis specimens were obtained (15 with chronic cholecystitis alone, 20 with chronic cholecystitis and gallstones) as controls. Histologically, the 35 specimens included 11 with normal gallbladder mucosa, 12 with mild atypical proliferation, 7 with moderate atypical proliferation, and 5 with severe atypical proliferation. All the above samples were fixed in 4% formalin, and 4 micron sections were prepared for immunohistochemistry studies.

For p-ERK1/2 and PI3-K detection, immunostaining was carried out using EnVision™ (ChemMate™EnVison +/HRP/DAB, Rabbit/Mouse Two Step Staining Method) according to the manufacture's protocol (DAKO laboratories Inc, California, USA). Briefly, paraffin-embedded gallbladder adenocarcinoma tissues were cut into 4 μm thick sections. The sections were de-paraffinized and incubated with 3% of H₂O₂ solution for 15 min, followed by EDTA-trypsinase digestion (0.125%, pH 9.0) for 15 min, then soaked with PBS (pH7.4) 3 times, each for 5 minutes. The pre-treated sections were then incubated with rabbit anti-human p-ERK1/2 or PI3-K (Bosite Inc, Wuhan, China) for 60 min at room temperature. Solution A (ChemMate™EnVison +/HRP) was added and incubated for another 30 min. Substrate DAB liquid was added and followed by hematoxylin counter-staining. Slides were dehydrated with different concentrations of alcohol and soaked in xylene for 5 minutes (3 times), and then mounted permanently with neutral balsam. Slides were examined independently by two pathologists. The results of p-ERK1/2 or PI-3K immunostaining were considered to be positive when more than 25% of the tumor cells were stained. The positive controls were provided by Bosite Inc, Wuhan.

The SPSS13.0 program was used for calculation of interrelationships between the analyzed p-ERK1/2 or PI3-K and histological or clinical factors by χ² independence test. Fisher's exact probability test was also used for analyzing statistical association between the two independent sample groups. The results were considered to be significant when the P value were less than 0.05. Disease specific overall survival analyses were determined and compared using the Kaplan-Meier method and the log-rank test. For multivariate analysis the Cox regression method was performed. 95% confidence intervals were used overall.

Immunohistochemistry for p-ERK1/2 and PI3-K were conducted with 108 gallbladder adenocarcinomas, 46 surrounding tissues of gallbladder adenocarcinoma, 15 adenoma polyps, and 35 chronic cholecystitis samples. Positive staining for p-ERK1/2 was observed in the cytoplasm and/or nucleus (Figure 1 and 2a–c). PI3-K staining was mostly seen in the cytoplasm as expected (Figure 1 and 2d–f). As shown in Table 1, of the 108 gallbladder adenocarcinomas, expression of p-ERK1/2 and PI3-K was detected in 63 (58.3%) and 55 cases (50.9%), respectively. In the 46 surrounding tissues of gallbladder adenocarcinoma, p-ERK1/2 and PI3-K were positive in 14 (30.4%) and 5 (10.1%) cases, respectively. Moderate to severe atypical hyperplasia were observed in all gallbladder mucous epithelium in p-ERK1/2 positive cases. In PI3-K positive samples, however, gallbladder mucous epithelium was normal in one case, mild atypical hyperplasia in one case, while moderate and severe atypical hyperplasia were seen in one and 2 cases, respectively. Positive staining for p-ERK1/2 and PI3-K was both observed in 3 out of 15 adenoma polyps which all showed moderate to severe atypical hyperplasia. In the chronic cholecystitis group, p-ERK1/2 and PI3-K staining was positive in 4 (11.4%) and 3 (8.6%) of the 35 cases, respectively. Gallbladder mucous epithelium in positive specimens showed moderate to severe atypical hyperplasia. Overall, the frequency of samples positive for p-ERK1/2 and PI3-K in gallbladder adenocarcinomas was significantly higher than that in surrounding tissues (χ²_pERK = 10.04, P < 0.01; χ²_PI3-K = 21.77, P < 0.01), in adenoma polyps (χ²_pERK = 7.78, P < 0.01; χ²_PI3-K = 5.06, P < 0.01), and in chronic cholecystitis (χ²_pERK = 23.35, P < 0.01; χ²_PI3-K = 19.67, P < 0.01).

We further analyzed the correlation of p-ERK1/2 and PI3-K expression with the clinical and pathological features of gallbladder adenocarcinoma. As shown in Table 2, the frequency of samples staining positive for p-ERK1/2 and PI3-K in cases with small tumor size (<2 cm in diameter), without lymph node metastasis, and no invasion of surrounding tissues was significantly lower than in cases with larger tumor size (>2 cm), lymph node metastasis, and invasion in surrounding tissues (P < 0.05 or P < 0.01). Interestingly, the positive staining for p-ERK1/2 in cases concomitant with gallstones/cholelithiasis was significantly higher than in cases without gallstones (P < 0.05). Moreover, positive staining for p-ERK1/2 and PI3-K in adenoma or well-differentiated adenocarcinomas was significantly lower compared to poorly-differentiated adenocarcinomas as shown in Table 3 (both, P < 0.01).

After surgical resection, only 67 out of 108 patients were able to be followed up via phone or mail surveys. Of the 67 cases with follow-up, 20 cases had over one year survival, and 47 died within one year after surgery, with a mean survival time of 9.6 ± 5.2 months. 37 of the 67 (55.2%) patients had positive immunohistochemical staining of p-ERK1/2, and 35 (52.2%) had positive PI3K staining. The relevance of positive p- ERK1/2 and PI3K expression to patients survival was examined by univariate Kaplan-Meier survival analysis. Overall survival was inversely associated with positive or increased expression of p-ERK1/2 (P = 0.045) (Figure 3a) and PI3K (P = 0.062) (Figure 3b). The relevance of overall survival and other clinical pathological characteristics were also assessed by univariate analysis which showed that the overall survival was associated with tumor pathological type (P = 0.031), tumor diameter (P = 0.003), lymph node metastasis (P = 0.005) and surrounding tissue invasion (P = 0.002). All factors that showed significant association in the univariate Kaplan-Meier analysis were subsequently subject to multivariate Cox regression survival analysis, which indicated that lymph node metastasis and surrounding tissue invasion were the most significant predictors of short overall survival, followed by p-ERK1/2 over-expression (Table 4).