Purpose: We aim to study certain histopathological characteristics of the retinoblastoma (RB) tumors in globes with clinically advanced RB, which can be correlated with the high-risk features including: tumor differentiation, growth pattern and focality. We also aim to reclassify the tumor pathologically in the analyzed cases according to the American Joint Committee on Cancer (AJCC) 8th edition in an attempt to compare the validity of this newest classification.
Methods: Retrospective study of patients diagnosed with clinical RB of groups D and E during the period: January 2013 to December 2017 at King Khaled Eye Specialist Hospital (KKESH) and King Abdulaziz University Hospital (KAUH). Charts were reviewed for demographic and basic clinical data. Histopathological features (tumor differentiation, growth pattern, focality, seeding, and presence of choroidal invasion (focal versus massive), level of optic nerve (ON) invasion, anterior chamber invasion, scleral and extra-scleral extension, and finally the documented pathological tumors (pT) classification based on the AJCC 7th edition were collected.
Results: We included 146 eyes with advanced retinoblastoma (groups D and E) from 104 patients. Gender distribution was almost equal with 54 males. Median age was 12 months (range 1-96 months), and a mean age was 17.1 ± 15.1 months. No family history was found in the majority (94.2%). Clinically, the most common presenting symptoms: leukocoria (73.3%), squint (33.6%) and least commonly proptosis (2.7%). A total of 106 enucleation specimens were reviewed. Degree of RB differentiation was: well differentiated (18%), moderate (30%), poor (35%), and undifferentiated (17%). The most common high-risk features were ON invasion (68%) with the majority being prelaminar in nature, choroidal invasion (45%) with more than half being massive, iris/trabecular meshwork (TM)/Schlemm's canal invasion (8.5%), and then intra-scleral/extra-scleral extension (5%). Less tumor differentiation doubles the relative risk of massive choroidal invasion (with 95% CI) with a statistically significant P value (P = 0.030). Endophytic RB was associated with vitreous seeding, while exophytic tumors were associated with subretinal seeding (P = 0.001) each. Ten cases with combined ON invasion (pre-laminar) and focal choroidal invasion were reclassified pT2a in the AJCC 8th edition instead of pT2b in the older 7th edition.
Conclusions: Our demographic and basic clinical data for advanced RB are comparable to other similar reports. The tumor growth pattern correlates well with the type of seeding observed in enucleated globes with RB. Less tumor differentiation is a relative risk of massive choroidal invasion. It is advocated to implement the AJCC 8th edition by ocular pathologists worldwide aiming to histopathologically classify the RB tumor in cases for selective adjuvant chemotherapy.
Keywords: Adjuvant chemotherapy; American Joint Committee on Cancer; Choroid; Classification; Extraocular; High-risk; Histopathology; Invasion; Optic nerve; Retinoblastoma; Sclera.