Procedure:
• Chemotherapy is administered prior to resection of the bony tumor.
• After surgery the gross specimen is thinly cross sectioned and carefully diagrammed.
• A cross-section of the tumor is divided into cassettes, decalcified and then processed for histologic sections.
• The percent of viable and necrotic tissue in each section is determined.
• All of the findings are combined to give a total amount of viable and necrotic tissue for the cross-section.
|
Percent Necrotic Tumor
|
Percent Viable Tumor
|
Grade
|
|
0%
|
100% (no response to chemotherapy)
|
I
|
|
< 50%
|
> 50%
|
IIA
|
|
50 - 95%
|
5 - 50%
|
IIB
|
|
> 95%
|
< 5%
|
III
|
|
100%
|
0%(no viable tumor)
|
IV
|
from: Children's Cancer Group and Pediatric Oncology Group (Coffin, 1999)
Interpretation:
• A good response to chemotherapy is considered >= 90% necrosis.
• Patients with >= 90% tumor necrosis have a 91% disease free survival.
• Patients with < 90% tumor necrosis have a 14% disease free survival.
Limitations:
• Histologic interpretation may be subjective.
• Highly atypical cells that are found scattered in reactive stroma are counted as viable tumor by convention, but their significance has not yet been completely determined.
• Improper processing such as over-decalcification may introduce technical artifacts.
