MODIFIED HISTOLOGIC GRADING OF NEUROBLASTOMAS BY REPLACEMENT OF MITOTIC RATE WITH MITOSIS KARYORRHEXIS INDEX - A CLINICOPATHOLOGICAL STUDY OF 223 CASES FROM THE PEDIATRIC-ONCOLOGY-GROUP

BACKGROUND. Histologic grading (HG) of neuroblastomas (NB) of prognost ic significance is based on the presence or absence of calcification a nd low mitotic rate (less than or equal to 10/10 high power fields). M itosis Karyorrhexis Index (MKI) is the main feature used for prognosti c categorization in Shimada classification and can be determined more readily than mitotic rate (MR). The purpose of this study is to test w hether MKI can be used instead of MR for histologic grading. METHODS. Low and intermediate MKI were lumped together as low MKI. We replaced MR with the modified MKI categories. The histologic grades for 223 NBs registered with the Pediatric Oncology Group protocols 8104 and 8441, were defined as follows: HG 1 = calcification + low MKI, HG 2 = calci fication or low MKI, HG 3 = high MKI and absence of calcification. Shi mada classification was also determined for comparison of modified HGs with favorable histology (FH) and unfavorable histology (UH), HGs wer e linked with age: low risk (LR) = HG 1 in all age groups + HG 2 in pa tients age younger than 1 year; high risk (HR) = HG 2 in patients age 1 year or older + HG 3 in all age groups. RESULTS, Statistically signi ficant differences in 5-year survival were seen in the NBs of differen t modified HG (1: 92.7%, 2: 74.9%, and 3: 18.2%) and risk groups (LR: 93.0% and HR: 47.9%) (P < 0.0001 and P = 0.0001, respectively). CONCLU SIONS. Pathologists may readily adapt to the modified HG described her e. Advantages of modified HGs include: (1) familiarity and reproducibi lity of MKI; (2) no need for linkage with age; and (3) a combination o f features used in original HGs and Shimada classification. (C) 1996 A merican Cancer Society.