Introduction:
Colorectal cancer invasion patterns at the tumor front reflect interactions between cancer cells and the surrounding stromal microenvironment. Two different invasion patterns are recognized: an infiltrative pattern, associated with aggressive tumor behavior, and an expansive pattern characterized by a prominent desmoplastic reaction with collagen fibre accumulation. Because collagen fibers are difficult to distinguish from smooth muscle tissue in routine hematoxylin–eosin staining, additional histochemical methods may improve their visualization.

Aim:
This pilot study aimed to evaluate the usefulness of Mallory trichrome staining in the histopathological assessment of collagen fibers at the colorectal cancer invasion front.

Material and methods:
Tissue samples from 126 patients who underwent surgical resection for colorectal cancer were analyzed. Based on hematoxylin–eosin staining, representative cases demonstrating a collagen-rich stromal reaction at the tumor margin were identified, and 25 selected samples were additionally examined using Mallory trichrome staining.

Results and Discussion:
Mallory staining enabled clear visualization and differentiation of collagen fibers from surrounding tissue structures, particularly smooth muscle layers, allowing a more precise identification of the desmoplastic reaction at the tumor invasion front. This method improved morphological assessment of the expansive pattern of tumor growth compared with routine hematoxylin–eosin staining alone.

Conclusions:
These findings suggest that Mallory trichrome staining may serve as a useful supplementary histochemical technique for evaluating stromal reactions in colorectal cancer. Improved identification of desmoplastic reaction may support more accurate characterization of tumor invasion patterns and contribute to improved pathological assessment.