Histopathological features and grading in rhabdomyosarcomas of childhood

Rhabdomyosarcoma represents a large group of soft tissue sarcomas displaying heterogeneous histopathological features. In addition to their histopathological classification, the variable expression of a number of histopathological features may contribute to the heterogeneity and may be related to prognosis. Tissue sections of 113 well‐documented, protocol‐treated patients with long term follow‐up (mean 6 years) were analysed by a panel of four paediatric pathologists. The following features were assessed: presence of rhabdomyoblasts, degree of maturation of rhabdomyoblasts, heterogeneous maturation patterns, mitotic activity, tumour necrosis, myxoid component, and septa. A scoring system was allocated to each index. High degree of maturation (amount of cytoplasm greater than surface area of the nucleus), absence of tumour necrosis (< 10% of tumour surface), and absence of septa (< 10% of tumour surface) significantly correlated with a favourable clinical course. Reproducibility in the assessment of these three features was good: mean κ varying from 0.53 to 0.64. A rhabdomyosarcoma score function for survival was defined by: (‐0.27 x degree of maturation score) + (0.007 x percentage septated area) + (0.031 x percentage tumour necrosis). Based on the score a two‐grade system was elaborated, i.e. grade I (score < ‐0.20) v. grade II (score < ‐0.20). Rhabdomyosarcoma grade appeared to be the best factor in predicting patients survival: 69% long‐term survival in patients with grade I v. 33% in patients with grade II (P= 0.0001). Moreover, this grading system was shown to have discriminative power within the group of patients with embryonal rhabdomyosarcoma: patients with a grade I tumour fared significantly better than those with a grade II tumour (63%v. 41% long‐term survival, P= 0.03). This study, therefore, demonstrated the prognostic value of this grading system and its useful application within the group of patients with embryonal rhabdomyosarcomas.