Based on Jass' criteria, adenocarcinomas are subdivided into:
• Well differentiated: made of simple or complex regular glands that preserve nuclear polarity and show nuclei of uniform dimensions (Fig. 1a).
• Moderately differentiated: made of simple or complex, regular or slightly irregular glands with alter ation or absence of nuclear polarity (Fig. 1b). • Poorly differentiated: made of highly irregular glands with loss of nuclear polarity or no gland formation (Fig. 1c).
Multivariate analysis has shown that histologic grade is a prognostic factor independent of stage [20, 26, 32].
To reduce the degree of interobserver variability in the grading of colorectal cancer a 2-tiered system has been proposed. This system is relatively easy and reproducible and is based solely on the presence of glands :
Low-grade carcinoma: greater than or equal to 50% gland formation.
High-grade carcinoma: less than 50% gland formation.
Signet-ring cell carcinoma, small cell carcinoma and undifferentiated carcinoma are considered high grade. Signet-ring cell and small cell carcinoma have shown a poor prognosis that is independent of stage .
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