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Table 1 Histological subtypes of colorectal adenocarcinoma, adapted from the 5th edition of the World Health Organization (WHO) classification of tumors of the digestive system [24]

From: Colorectal liver metastases: radiopathological correlation

Mucinous Adenocarcinoma > 50% of pools of extracellular mucin in tumors.
Signet-ring cell carcinoma Presence of > 50% of tumor cells with signet ring cell (prominent intracytoplasmic mucin vacuole that pushes the nucleus to the periphery). Poorly differentiated and poor outcome.
Medullary carcinoma Extremely rare. Sheets of epithelioid neoplastic cells with large vesicular nuclei, prominent nucleoli, and abundant cytoplasm. Associated with microsatellite instability and a better prognosis.
Serrated adenocarcinoma Glandular serration that can be associated with mucinous areas.
Micropapillary adenocarcinoma > 5% of the tumor showing small clusters of tumors cells with stromal spaces mimicking vascular channels
Adenoma-like adenocarcinoma > 50% of invasive areas showing an adenoma-like aspect.
Adenosquamous Characteristics of both adenocarcinoma and squamous cell carcinoma.
Carcinoma with sarcomatoid component Undifferentiated with sarcomatoid aspects including spindle cell components or rhabdoid features.
Undifferentiated Absence of morphological, immunohistochemical or molecular differentiation other than epithelial tumor.