What are the histopathological growth patterns?
Histopathological growth patterns (HGPs) of liver metastases reveal the intricate interactions between cancer cells and the hepatic microenvironment during metastatic growth. These distinct patterns can be visualized using light microscopy on hematoxylin and eosin-stained tissue sections, specifically at the tumor-liver interface. Notably, the presence of specific HGPs is not confined to any particular primary tumor type; rather, they have been observed across a wide spectrum of cancers metastasizing to the liver, including colorectal, breast, pancreatic, and melanoma. The ubiquity of HGPs across various cancer types suggests fundamental and conserved mechanisms governing cancer cell interactions with their cellular and molecular surroundings. This universality extends beyond liver metastases, as similar growth patterns have been identified in primary liver cancers, lung metastases, and primary lung tumors. Such widespread occurrence underscores the significance of HGPs in understanding the broader principles of tumor growth and adaptation to diverse tissue environments.
Why are the histopathological growth patterns important?
The clinical value of histopathological growth patterns of liver metastases is well-established, particularly for colorectal cancer, and extends to other tumor types such as breast cancer and melanoma. Two main HGPs have been consistently identified across various cancer types: the encapsulated pattern (formerly known as desmoplastic) and the replacement pattern.
Regardless of the primary tumor origin and independent of other established prognostic factors, the encapsulated HGP is associated with better outcomes compared to the replacement HGP, independent of pre-surgery treatment. Moreover, the replacement growth pattern is associated with resistance to systemic treatment, including chemotherapy with or without bevacizumab. This growth pattern also indicates disease that is not limited to the liver.
The morphological and clinical distinctions among growth patterns are intrinsically linked to underlying biological differences. The known differences between replacement and encapsulated growth patterns in liver metastases include lower differentiation grade, vessel co-option instead of angiogenesis, higher glucose metabolism, increased cancer cell proliferation and an “immune desert” phenotype in the replacement pattern versus the encapsulated pattern.
A deeper understanding of the unique biological characteristics associated with each growth pattern has the potential to pave the way for novel therapeutic approaches. These innovative strategies could be tailored to address the specific interactions between cancer cells and liver tissue, ultimately leading to more targeted and effective treatments of patients with liver metastasis.
Introductory remarks on assessing the histopathological growth pattern of liver metastases
- The growth pattern is a histological parameter assessed by light microscopic imaging of good quality hematoxylin and eosin-stained sections of formalin-fixed paraffin-embedded (FFPE) tissue of resection specimens of liver metastases.
- The growth pattern is a characteristic of the tumor–liver interface, more specifically the interface with the adjacent non-tumorous hepatic lobular tissue. The center of the metastasis does not contribute to the classification of a growth pattern.
- Tissue cores from needle biopsy procedures are not suitable for HGP assessment.
- Resection specimen tissue sections with only a limited part of the tumor–liver interface are considered insufficient to assess the growth pattern of liver metastases.
- Also, if no viable tumor tissue is present in the metastasis, the growth pattern cannot be assessed.
- Delayed fixation, surgical cautery or radiofrequency ablation artifacts may lead to insufficient quality of the tissue sections for scoring the growth patterns.
- When more than one growth pattern is present in a metastasis, the relative fractions of each growth pattern as a percentage of the total length of the interface are estimated.
References for the introductory page
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