Frequent alterations in the expression of tumor suppressor genes p16INK4A and pRb in esophageal squamous cell carcinoma in the Indian population

Purposes: Alterations in the cell cycle regulatory p16(INK4a)/Cyclin D1/pRb pathway play a pivotal role in tumorigenesis. Knowledge of alterations in the tumor suppressor protein pRb and its negative regulator, p16(CDKN2/MTS1/INK4a) in esophageal squamous cell carcinoma (ESCC) from the Indian subcontinent is meager. To gain insight into the mechanisms underlying tumorigenesis and to search for diagnostic molecular markers ESCC, we analyzed the expression of p16(INK4a) and pRb in ESCCs in the Indian population. Methods: Immunohistochemical analysis of pRb and p16(INK4a) proteins was carried out in paraffin-embedded sections from 61 surgically resected ESCCs and matched normal tissues, and the results correlated with clinicopathological parameters using chi square and Fisher's exact tests. Dual immunohistochemical analysis has been carried out to demonstrate the concomitant loss of expression of p16(INK4a) and pRb. Results: Fifty-nine of 61 (97%) cases showed aberration(s) in either or both of these proteins confirming their critical role in esophageal tumorigenesis. Loss of pRb was observed in 51 of the 61 (84%) and loss of p16(INK4a) was observed in 35 of 61 (57%) cases. Loss of pRb showed significant association with dedifferentiation of the tumor (P = 0.004), p16(-)/pRb(-), and p16(+)/pRb(-) phenotypes were significantly associated with nodal metastasis (P = 0.017 and 0.027, respectively), while p16(-)/pRb(+) phenotype was associated with dedifferentiation of the tumor (P = 0.012). Conclusion: pRb/p16(INK4a) pathway plays a critical role in esophageal tumorigenesis in the Indian population. The dual hits (concomitant loss) of pRb and p16(INK4a) expression suggest that these two components are not mutually exclusive, and can both be altered in a significant proportion of primary ESCCs serving as putative diagnostic markers for esophageal cancer. However, the impact of dual. hit on tumor behavior and disease prognosis remains to be determined.