[479] Implications of the 2009 AJCC Melanoma Staging and Classification System for Thin Melanomas

Vicki H Chu, Michael T Tetzlaff, Victor G Prieto, Carlos Torres-Cabala, Roland Bassett, Michael S McLemore, Doina Ivan, Wei-Lien (Billy) Wang, Jonathan L Curry. Baylor College of Medicine, Houston, TX; MD Anderson Cancer Center, Houston, TX

Background: The TNM staging system for cutaneous melanomas has been revised in the 7th edition of the AJCC staging and classification system. Mitotic rate for thin melanomas was determined to be a stronger predictor of disease free survival and has replaced Clark level of invasion in defining T1 lesions. In addition, a single isolated tumor cell in a sentinel lymph node was determined to be sufficient for defining stage III disease. We report the impact of the new classification system in defining T1 lesions and the status of sentinel lymph node (SLN) biopsy.
Design: The surgical pathology database was searched for cutaneous melanomas from January 1, 2010 to June 30, 2011. Invasive melanomas were reviewed by dermatopathologists with all reported histologic features included in the analysis. 340 cases were identified of which 139 had Breslow thickness ≤ 1.0 mm. The 139 cases were categorized according to the 2001 and 2009 AJCC classification system. Clark level (CL), Breslow thickness (BT), mitosis (M), ulcer (U), and SLN status was collected. Comparison between groups were made using t-tests.
Results: T1 lesions were redistributed in 41/139 cases according to the 7th edition of AJCC classification system. 18 T1b cases with CL < 4 were identified based on the presence of only mitosis. These cases would have been defined as T1a under the 6th edition. 23 cases with CL ≥ 4 were redistributed to T1a due to absence of mitosis. 46/60 T1b cases had SLN biopsy. 6/46 cases had positive SLN in which metastatic melanoma was detected in 8/11 SLNs examined. 5/8 positive SLNs demonstrated isolated tumor cells (less than 15 melanoma cells) and one SLN with a single positive tumor cell. None of 18 redistributed T1b cases had a positive SLN. Mean BT in lesions categorized as CL 2/3 -M/-U was signigicantly lower (p<0.0001).

Distribution of Thin Melanomas
 2001 AJCC, 6th Edition2009 AJCC, 7th Edition ( '*' = +SLN)Mean Breslow Thickness (mm)
CL 2/3 -M/-U5605600.42†
CL 2/3 +M/-U1800180.72
CL 2/3 -M/+U0101 (1*)0.64
CL 2/3 +M/+U04040.77
CL 4/5 -M/-U0232300.60
CL 4/5 +M/-U036036 (4*)0.74
CL 4/5 -M/+U0101 (*1)0.60
CL 4/5 +M/+U00000

Conclusions: The 7th edition of the AJCC staging system redefined nearly 30% T1 lesions in our sample. The number of T1a cases increased by 5 with a commensurate decrease in T1b cases by 5. The total number of T1b lesions was lower and thus fewer cases met the criteria for SLN biopsy. Cases with positive SLN were defined as T1b according to the 2001 and 2009 classification system.
Category: Dermatopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 97, Wednesday Afternoon


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