**1. Introduction**

Colorectal cancer (CRC) is one of the commonest malignancies affecting both males and females. It is the second leading cause of cancer-related death in the Western industrialized world. The incidence of colorectal cancer increases with age, with nearly two-thirds of patients diagnosed aged over 65 years. Colorectal cancer (CRC) is the third most frequent tumor, which affects the inhabitants of developed and developing countries. Among males, CRC comes after lung and prostate tumors; among females it follows breast cancer,

occupying the second place in terms of incidence [1]. As a result of early detection of colonic polyps by screening and removal before they can develop into outright cancer, death rates have been dropping. In addition, screening and treatment for colorectal cancer at early stages have improved over the last several decades, resulting in increasing number of survivors of colorectal cancer.

Vitamin D is a secosteroid. Though it is named a vitamin, it is rather recognized as a prohormone given its synthesis in the skin and the multiple systemic actions of its metabolites [2]. In 1980, Garland brothers had suggested that vitamin D could be a protective factor against colorectal cancer, based on their observation of geographic distribution for colorectal cancer mortality in regions where population was less exposed to sunshine [3]. Few years later, the same authors confirmed this association, by reporting an inverse correlation between vitamin D status and CRC [4]. Different studies in the upcoming years [5–7] have also confirmed the relationship between plasma 25-hydroxyvitamin D concentrations and risk of colorectal cancer.

Many epidemiological studies have shown a negative association between colorectal cancer incidence and vitamin D levels [4, 7], as well as colorectal cancer risk and calcium intake [8, 9]. 1,25-Dihydroxyvitamin D3 directly affects growth factor and cytokine synthesis and signaling in colonic epithelium and modulates the cell cycle, apoptosis, and differentiation [10]. 1,25(OH)2 D3 exerts its biological effects by binding to the vitamin D receptor (VDR), thereby regulating gene expression. The active metabolite has prominent antiproliferative, anti-angiogenic, and pro-differentiating action in a wide range of tumor cells due to the VDR being expressed in almost all tissues. Several important cellular signaling pathways can thus be acted upon. However, for clinical trials, the problem remains of how to administer side effect-free doses of 1,25(OH)<sup>2</sup> D3 [11].

A frequently measured range for serum levels of 25OHD3 in adults is 10–50 ng/ml. Intestinal calcium absorption is optimized at levels above 30–32 ng/ml. Parathyroid hormone levels start to rise at 25OHD levels below 30 ng/ml, marking vitamin D insufficiency [12]. Numerous investigations reported an increased risk for colorectal cancer in individuals with 25OHD3 blood levels below 12 ng/ml [13, 14].

In kidney cells, 25OHD is converted by the hydroxylase into the active metabolite 1,25(OH)2 D3 . However, also other cell types, such as colonocytes, express vitamin D hydroxylases [15], indicating an autocrine/paracrine function of the active metabolite. Low serum 25OHD3 precursor levels could result in colonic 1,25(OH)2 D3 production that is insufficient for maintenance of autocrine/paracrine regulation of cellular growth and function [16].

It has been suggested that the antitumoral action of 1,25(OH)2 D3 in colorectal cancer relies on several mechanisms at the cellular level, such as inhibition of cell proliferation, sensitiveness to apoptosis, induction of epithelial differentiation, cell detoxification metabolism, inhibition of angiogenesis, and cell-cell adhesion [2]. This prompted us to evaluate immunohistochemical expression of beta-catenin and PAK1 (which are involved in Wnt-beta-catenin pathway) as well as expression of p53 and Ki67 (markers of apoptosis and cell proliferation, respectively) in colorectal polyps and cancer. We therefore studied for the first time the relationship between histological type and grade of colorectal tumors with the expression of these markers and attempted to correlate these results with vitamin D blood levels.
