American Joint Committee on Cancer (AJCC) Classification of Iris Melanoma: Comparison between 7^th and 8^th Edition based on 432 cases

Abstract

Purpose : To classify 432 cases of primary iris melanoma in accordance with 7^th and 8^th edition of American Joint Committee on Cancer (AJCC) Staging Manual and to compare the two editions, in order to assess similarities and differences in case distribution.

Methods : A retrospective case series of 432 patients with primary iris melanoma was performed. Charts were reviewed in order to assess primary tumor (T), regional lymph node (N) and distant metastasis (M) status in accordance with the definitions proposed in 7^th and 8^th edition of the AJCC Staging Manual. Both clinical and pathological findings (when available) were taken into account for classification purposes. Inclusion criteria required a diagnosis of primary iris melanoma, and tumors in which less than one-half the lesion volume was located in the iris were excluded, as they may have had originated in the ciliary body. Continuous variables were reported using medians, interquartile ranges (IQRs), and ranges. Categorical variables were reported with frequencies.

Results : Median follow up for 432 patients was 1.9 years (IQR, 0.3-6.3 year; range, 0-34.4 years). A comparison of tumor classification ([7^th] vs. [8^th] edition) by T category revealed no differences between the two editions and distribution were as follows: T1 (324, 75%), T2 (83, 19%), T3 (2, <1%), and T4 (23, 5%). Comparison by T subcategory revealed changes: T1a ([193, 45%] vs [193, 45%]), T1b ([66, 15%] vs [66, 15%]), T1c ([65, 15%] vs [65, 15%]), T2a ([30, 7%] vs [51, 12%]), T2b ([na] vs [2, <1%]), T2c ([na] vs [30, 7%]), T3a ([0, 0%] vs [na]), T4a ([23, 5%] vs [23, 5%]), T4b ([0, 0%] vs [0, 0%]). All patients (432) were staged N0 and M0 at date first seen.

Conclusions : The AJCC 8^th edition classification for iris melanoma presents minimal changes compared with 7^th edition. Main differences in distribution were found in categories T2 and T3. The more recent 8^th edition differentiates category T2 with regards to invasion of ciliary body only (T2a) and both ciliary body and choroid (T2b). Furthermore, it eliminates T3a category because of the small number of iris melanomas that fall into this category. Categories T1 and T4 remained unchanged. The authors believe that continuous update of internationally recognized cancer staging systems is important, as they are tools for uniform prognostic prediction.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.