Ueno H et al. (2008) Histological grading of colorectal cancer: a simple and objective method. Ann Surg 247: 811–818

The TNM and WHO classification systems grade tumors into four categories according to degree of cell differentiation; however, the grades are defined on the basis of subjective judgment, which can differ between clinicians. A major problem with these systems is that the definition of the least differentiated tumor grade has not been standardized. Ueno and colleagues, therefore, considered how the extent of poor differentiation could be used to grade tumors and predict patient outcomes.

Data were analyzed from 1,075 Japanese patients (average age 62 years, 624 male) with advanced colorectal cancer who underwent tumor resection. Poorly differentiated regions were defined strictly as those with no glandular structure. Grade categories were based on the total area of poorly differentiated cells, as viewed under a microscope: tumors with <10 clusters of ≥5 poorly differentiated cells were classified as grade I (161 patients); tumors with ≥10 such clusters as grade II (575 patients); and tumors with poorly differentiated cells covering the entire microscopic field at 40 × magnification as grade III (339 patients). Patients with grade I tumors had the best prognosis, with a 99.3% 5-year cancer-specific survival rate, compared with 86.0% and 68.9% for grade II and III tumors, respectively.

In comparison with the WHO and TNM grading systems, which define poorly differentiated tumors as those with 'some' gland formation or mucin production, Ueno et al. believe that quantification of regions without glandular formation provides objective results, and could be a practical system for tumor grade standardization and selection of optimal postoperative therapy.