Histopathological grading of soft tissue tumours. Prognostic significance in a prospective study of 278 consecutive cases.

A consecutive 10-year series of 278 soft tissue sarcomas was prospectively graded, using a system based on the number of mitoses and taking into account parameters such as cellularity, anaplasia, necrosis, and histogenetic type and subtype of tumour. Prognostic factors in relation to metastasis-free survival were studied by uni- and multivariate analysis. Fifty-seven (20.5 per cent) were low-grade tumours, 43 (15.5 per cent) were intermediate, and 178 (64 per cent) were high grade. High-grade tumours were divided into two groups; 80 (29 per cent) grade 3A (= 5-20 mitoses per 10 high power fields (HPF)) and 78 grade 3B (28 per cent) (= more than 20 mitoses/10 HPF); 10 HPF corresponds to 2.5 mm2. Twenty (7.2 per cent) high-grade tumours could not be further subdivided. Grading was found to be the prognostic factor associated with the strongest predictive value. Five-year survival in low-grade and intermediate tumours (95 and 86 percent, respectively) differed significantly (P less than 0.0001) from high grade (50 per cent) and (p = 0.0018) between grade 3A (64 per cent) and grade 3B (41 per cent). Other prognostic indicators of importance in high-grade tumours were age, local recurrence at presentation (primary operation outside the Centre), and localization (superficial vs. deep).