Myofibroblasts of the muscle layer stimulate the malignant potential of colorectal cancer

Abstract

Myofibroblasts of colorectal cancer (CRC) have been associated with histopathological factors such as lymph node metastasis, liver metastasis and local recurrence. However, few studies have assessed the association between these malignant potentials and the myofibroblast distribution in CRC. We aimed to evaluate the relationship between clinical factors and myofibroblast distribution around CRC invasive lesions. The study included 121 cases of pT3 CRC that were diagnosed at stage II or III. Myofibroblast density of the following three histological layers was measured: the submucosa (SM), muscularis propria (MP) and subserosa (SS). We analyzed the relationship between the clinicopathological factors and myofibroblast density by studying the histopathological features of the three layers. The myofibroblast density of the MP layer was significantly higher in the groups with high-frequency lymphatic and venous invasion than the groups with low-frequency lymphatic (P<0.001) and venous (P<0.01) invasion, respectively. In the positive lymph node metastasis group, the myofibroblast density at the MP layer was significantly higher than that in the negative lymph node metastasis group (P<0.001). The high myofibroblast density group at the MP layer was significantly associated with poor overall survival (P<0.003). Our study indicated that myofibroblasts are a type of cancer-associated fibroblasts and that the myofibroblast distribution contributes to the malignant potential of CRC. Furthermore, we demonstrated that myofibroblasts present at the MP layer play an important role in the malignant potential and poor prognosis of patients with CRC.

Figure 1

The expanding and infiltrating types of colorectal cancer, which invaded through the mucosa to the subserosa. The expanding type was recognised as the overall pushing growth type of adenocarcinoma and the invasive margin was clear (A). The infiltrating type was recognised as the widespread streaming form of adenocarcinoma (B). Histology of the expanding type (C) and the infiltrating type (D) around the tumor invasive lesion in the muscularis propria layer. M, mucosa; SM, submucosa; MP, muscularis propria; SS, subserosa.

Figure 2

Representative case of the myofibroblast distribution in each invasive level of colorectal cancer. Myofibroblasts exist around the invasive front of each colorectal histological wall level (A). We identified the colorectal cancer invasive lesions using hematoxylin and eosin staining and selected the paraffin-embedded specimen that showed three invasive lesions in each histological layer (SM, MP and SS) (B–D). M, mucosa; SM, submucosa; MP, muscularis propria; SS, subserosa.

Figure 3

Representative case of an invasive lesion of the muscularis propria layer: α-SMA (A), the binarisation image of α-SMA (B), hematoxylin and eosin staining (C), desmin (D), the binarisation image of desmin (E) and subtraction image (α-SMA-desmin) (F). α-SMA, α-smooth muscle actin.

Figure 4

The mean myofibroblast density in each invasive level of colorectal cancer. The association between the invasive type (expanding and infiltrating) and myofibroblast distribution (A). The association between the lymphatic invasion and myofibroblast distribution (B). The association between venous invasion and myofibroblast distribution (C). The association between lymph node metastasis and myofibroblast distribution (D). Values are given as the mean ± standard error of the mean. ^*P<0.05, ^**P<0.01 and ^***P<0.001. ns, not significant. SM, submucosa; MP, muscularis propria; SS, subserosa.

Figure 5

The association between the myofibroblast density of each invasive wall level and overall survival of patients with colorectal cancer. There was no significant difference between the high and low myofibroblast density groups in both the SM and SS invasive wall levels (A and C). There was a significant difference between the high and low myofibroblast density groups in the MP invasive wall level (B). SM, submucosa; MP, muscularis propria; SS, subserosa.