Abstract 640: Histopathologic and molecular features in a subset of pilocytic astrocytomas in a tertiary African hospital
Authors: Nweke Michael C. , Ogun Gabriel O. , Okolo Clement A. , Adeleye Amos D. , Adesina Adekunle M. 
Published: August 2018

Background: Pilocytic astrocytomas are WHO grade I astrocytomas. Worldwide, they have been documented to be the second most common gliomas after WHO grade IV glioblastomas. Definitive diagnosis may be made with traditional hematoxylin and eosin. Increasingly, a number of cases are atypical deceptive in clinical and histopathologic presentation, requiring ancillary immunohistochemical and molecular studies. This study evaluated a subset of pilocytic astrocytomas at the University College Hospital Ibadan. Nigeria.

Methods: All cases of Pilocytic Astrocytomas were identified retrospectively within our institutional database over a 12-year period. Inclusion criteria was by availability of the FFPE block. Astrocytic origin was confirmed by GFAP immunohistochemistry; previously stained hematoxylin and eosin slides were reviewed with newly re-sectioned hematoxylin and eosin stained slides along with ancillary Ki-67/MIB immunohistochemistry labelling index. ATRX immunohistochemistry was carried out on all re-sectioned slides. Tissue scrolls were taken for DNA extraction and pyro-sequencing for BRAFV600E BRAF mutation using a Qiagen pyrosequencer. This work was carried out in the molecular neuropathology laboratory at the Texas Children's Hospital, Houston Texas. Results were analyzed using SPSS version 24.

Results: 40 cases (30.7%) of all astrocytic neoplasms were documented over this 12-year period. 23(57.5%)of these cases were suitable for analysis in this study. Males accounted for 65.2% of cases. Male: female ratio was 1:0.5. The mean age of all the cases was 14.22+/- 12.90 years, median age of 8 years with an age range of 42 years. 65.2% of all cases were within the 0-15-year age group, 17.4% were within the 16 - 30-year age group while the remaining 17.4% were within the 31 - 45-year age group. Most cases occurred infratentoriallysupratentorially (69.6%). The cerebellum was the commonest location accounting for 47.8%, followed by the supra-sellar region (17.4%). Most cases were centrally sited (47.8%). All cases (100%) showed positive ATRX expression. 3 cases (20%) of BRAF V600E expression were recorded. This included 1 case with malignant/anaplastic features which was previously misdiagnosed as a glioblastoma with suggestive radiologic imaging. Mean age of tumors with BRAF positive expression was 13.95 +/- 12.95years, while the mean age for BRAF negative cases was 17.00 +/-16.97 years. The difference between these ages was not statistically significant.

Limitations: The quality of available blocks limited DNA amplification and further analysis in 8 of the cases.

Conclusion: This study aims to underscores the importance of BRAF V600E mutations among pilocytic astrocytomas in our environment with regards to its diagnostic and prognostic significance.

Citation Format: Michael C. Nweke, Gabriel O. Ogun, Clement A. Okolo, Amos D. Adeleye, Adekunle M. Adesina. Histopathologic and molecular features in a subset of pilocytic astrocytomas in a tertiary African hospital [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 640.