Colorectal adenoma stem-like cell populations: associations with adenoma characteristics and metachronous colorectal neoplasia

Abstract

Cancer stem cells have tumor-initiation and tumor-maintenance capabilities. Stem-like cells are present in colorectal adenomas, but their relationship to adenoma pathology and patient characteristics, including metachronous development of an additional adenoma ("recurrence"), has not been studied extensively. We evaluated the expression of aldehyde dehydrogenase isoform 1A1 (ALDH1A1), a putative stem cell marker, in baseline adenomas from the placebo arm of chemoprevention trial participants with colonoscopic follow-up. An exploratory set of 20 baseline adenomas was analyzed by ALDH1A1 immunohistochemistry with morphometry, and a replication set of 89 adenomas from 76 high-risk participants was evaluated by computerized image analysis. ALDH1A1-labeling indices (ALI) were similar across patient characteristics and in advanced and nonadvanced adenomas. There was a trend toward higher ALIs in adenomas occurring in the right than left colon (P = 0.09). ALIs of synchronous adenomas were correlated (intraclass correlation coefficient 0.67). Participants in both sample sets who developed a metachronous adenoma had significantly higher ALIs in their baseline adenoma than participants who remained adenoma free. In the replication set, the adjusted odds for metachronous adenoma increased 1.46 for each 10% increase in ALIs (P = 0.03). A best-fit algorithm-based cutoff point of 22.4% had specificity of 75.0% and positive predictive value of 70.0% for metachronous adenoma development. A larger population of ALDH1A1-expressing cells in an adenoma is associated with a higher risk for metachronous adenoma, independent of adenoma size or histopathology. If confirmed, ALDH1A1 has potential as a novel biomarker in risk assessment and as a potential stem cell target for chemoprevention.

Figure 1. Examples of ALDH1A1 stem-like cell marker expression by immunohistochemistry in control colorectal mucosa and in baseline adenomas in relation to metachronous adenoma development (“recurrence”)

In non-neoplastic mucosa, the epithelial stem-like cells (arrows) are located near the bases of crypts (Panel A, with higher magnification in Panel B). In contrast, the stem-like cells in adenomas (Panels C through F) are distributed throughout the neoplastic glands, with smaller numbers near the luminal surface than in the deeper glands. An advanced adenoma with low-grade dysplasia but size greater than 1 centimeter in a participant who developed a metachronous adenoma (Panels C and E) has numerous ALDH1A1-positive stem-like cells, in contrast to an advanced adenoma with low-grade dysplasia that has only scattered stem-like cells (arrows) in a participant who was adenoma-free at follow-up (Panels D and F).

Figure 2. Topographical Expression of ALDH1A1 in 19 polyps in relation to metachronous adenoma development

ALDH1A1 labeling index by manual immunohistochemistry and morphometric analysis is shown for each subject. The ALDH1A1 labeling index for each of the four topographic sites (lower third, middle third and upper third of crypts and surface epithelium) is shown for non-advanced adenomas (red dots) and advanced adenoma (black dots) grouped by development of a subsequent adenoma. The subjects with a metachronous adenoma have significantly higher median ALDH1 values (indicated by +): 53.8% vs. 11.9%, p=.002, for deep glands; 34.5% vs. 6.7%, p=.002, for middle glands; 16.3% vs. 2.4%, p=.002, for upper glands; 8.2% vs. 2.1%, p=.03, for surface epithelium.

Figure 3. Percentage of ALDH1A1-expressing stem-like cells in 89 baseline non-advanced and advanced adenomas in replication set

ALDH1A1 labeling index by automated immunohistochemistry and computerized image analysis is shown for each adenoma (lesion-level data). Multiple adenomas in individual participants are connected by lines and have similar intra-subject indices in 9 of 11 subjects (intra-class correlation coefficient 0.67). The median ALDH1A1 labeling indices for the non-advanced and advanced adenoma subgroups are indicated by the plus signs, and are not statistically significantly different: 9.3% for non-advanced adenomas and 15.9% for advanced adenomas.

Figure 4. Percentage of ALDH1A1-expressing stem-like cells in 89 baseline adenomas of subjects without and with metatchronous adenoma at follow up colonoscopy (recurrence) in replication set

ALDH1A1 labeling index by automated immunohistochemistry and computerized image analysis is shown for each adenoma (lesion-level data). Multiple adenomas in individual participants are connected by lines and have similar indices in 9 of 11 subjects (intra-class correlation coefficient 0.67). The median ALDH1A1 labeling indices for the non-advanced and advanced adenoma subgroups (group level data) are indicated by the plus signs. The subjects with a metachronous adenoma have significantly higher values: 23.0% as compared to 8.6% for subjects who remained adenoma-free (p <0.05).