Cell Cycle Regulators in Pheochromocytomas (PCTs) and Paragangliomas (PGLs) and Correlation with SDHx Status and FGFR4 Genotype
Clarissa A Cassol, Sylvia L Asa. University Health Network, Toronto, ON, Canada
Background: Proliferation and apoptosis evasion are hallmarks of cancer. Cell cycle (CC) regulators (cyclins and CDKs) promote CC progression through Rb inactivation, while CC inhibitors such as p16, p21, p27, p53 and p57 prevent it. In this study, we investigated the expression of CC regulators and inhibitors in PCTs/PGLs and correlated the results with SDHB IHC and FGFR4 G388R genotype.
Design: PCTs (N=39) and PGLs (N=76) from 115 patients of known FGFR4-G388R genotype were assembled in a TMA stained with antibodies against p16, p21, p27 KIP1, p53, Ki67, Cyclin D1, Rb and SDHB. TMA slides were scanned and analyzed using Spectrum Plus (Aperio). Immunostaining scores and outcomes were used for exploratory statistical analysis on SPSS 11.0.
Results: In 115 patients, there were 13 outcomes - 4 local recurrences, 7 metastases and 2 deaths - all from PGLs. SDHB IHC showed loss in 46 cases, of which only one was a PCT. All but one metastasis occurred in SDHB IHC-negative cases. The CC inhibitors p16 (p=0.002), p27 (p=0.001), p21 (p=0.044) and Rb (p=0.007) were overexpressed in PGLs compared to normal adrenal medulla. Conversely, they were underexpressed in PCTs, with exception of p16, which was also overexpressed (p<0.001). The percentage of p53 positive nuclei was very low in both PCTs (3%),PGLs (1.2%), and normal adrenal medullas (2.5%). MIB1 was overexpressed in PGLs (4%) when compared to PCTs (0.8%, p<.0001) and normal medulla (1.3%, p=0.004); it was also associated with an increased risk for metastasis (p=0.008). The percentage of cells with cytoplasmic staining for p27 was higher in metastatic cases (53.5% versus 39%, p=0.045), as was MIB1 nuclear staining (5.8% versus 2.5%, p=0.002). The percentage of Cyclin D1 nuclear staining was higher in FGFR4 Gly388 cases (70%) than in FGFR4 Arg388 (60%), p=0.002; while the percentage of p53 nuclear staining was lower (p=0.014). Comparison between SDHB-positive and -negative tumors showed significant underexpression of p16 in SDHB negative cases (p=0.014) and overexpression of Cyclin D1 (p=0.004) and MIB1 (4.3% versus 1.7%, p<0.001).
Conclusions: The different patterns of expression of cell cycle inhibitors between PGLs and PCTs reflect their different biology and behavior and warrant further investigation. The low percentage of p53 staining is in accordance with previous studies showing a very low frequency of p53 mutations in these tumors. SDHB-negative and FGFR4 Gly388 cases seem to have higher proliferative activity. A high MIB1 index was significantly associated with malignancy, as well as with SDHB loss.
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 51, Tuesday Afternoon