CCND1 and lip and oral cavity carcinoma: Studies associating cyclin D1 expression and oral cancer prognosis are warranted to better ensure ample sample size with varying in the study population, better control for potential confounders (e.g., using the same IHC methodology and cut-off value) and to take into account the interaction between cyclin D1 expression and environmental factors or personal habits (e.g., cigarette smoking, alcohol abuse, areca quid chewing).