Estimating Tumor Volume Reduction in the Breast After Neoadjuvant (a.k.a. Pre-Operative) Therapy - Magee Method
Description
Ideally, one should use tumor size in all 3 dimensions for the most accurate determination of tumor volume reduction. However, accurate
measurement of all 3 tumor dimensions are rarely available, therefore, the standard method described below for estimating tumor size/volume
reduction uses the largest tumor dimension. Gross evaluation of the specimen is extremely important. The largest dimension of the gross tumor
bed/fibrotic area should be specifically noted in the gross description of the pathology report. This area should be either entirely submitted
(if small i.e. ≤ 3 cm) or sampled extensively (if large, i.e. > 3 cm), with sections serially submitted at 0.5 cm interval along the
largest dimension. The entire region needs to be submitted regardless of the size if no tumor was detected on initial sections. The tumor
cellularity of the resection specimen should be compared with the pre-therapy biopsy. Specifically, the pre-therapy biopsy should be screened
for
de novo sclerosis and necrosis. If these areas are present in pre-therapy biopsy, then similar areas in post-therapy resection
specimens should not be counted towards therapy related changes. After excluding these
de novo changes, the resection specimen showing
treatment related fibrosis should be compared to the cellularity of pre-therapy biopsy and the residual cellularity of the tumor bed is
estimated. The therapy related stromal changes often have fibroelastosis rather than pure fibrosis. The revised tumor size is calculated by
multiplying the largest dimension of gross tumor bed/fibrotic area with the tumor cellularity (compared to pre-therapy biopsy) of the resection
specimen. The percentage tumor size/volume reduction is calculated by subtracting revised tumor size from pre-therapy size, divided by pre-therapy
size times 100 (use worksheet below). Although this method may also be used for determining amount of response within the lymph nodes, the lack of
accurate pre-therapy lymph node metastasis size precludes this application. However, presence or absence of tumor within lymph nodes at post-therapy
resection specimen is enough to judge if pathologic response was complete or incomplete. Although immeasurable, if residual tumor is identified only
in vascular spaces, the pathologic response should be considered as incomplete. However, this is an extremely rare phenomenon and if thorough
examination of the breast is performed, generally an intraparenchymal component is also identified. In cases of inflammatory carcinoma where
pre-therapy size is not available, the size of tumor-bed/fibrotic area on gross exam can be used to estimate the pre-therapy size.
Reference
Bhargava R, Dabbs DJ, Beriwal S, Yildiz IA, Badve P, Soran A, Johnson RR, Brufsky AM, Lembersky BC, McGuire K, Ahrendt GM. Semiquantitative
hormone receptor level influences response to trastuzumab containing neoadjuvant chemotherapy in HER2 positive breast cancer. Mod Pathol.
2011;24:367-374.
PMID: 21102420.
Link at Modern Pathology
Worksheet
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Revised tumor size after correcting for cellularity
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Estimated Primary Tumor Volume Reduction
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