Objective:To investigate the clinicopathological and molecular genetic features of high-grade astrocytomas with piloid features (HGAP).Methods:Clinical, histopathological and imaging data of 7 cases of HGAP diagnosed at the Neuropathology Center of Beijing Tiantan Hospital, Beijing, China from August 2023 to October 2024 were collected. The histopathological and molecular features for each case were analyzed.Results:Among the seven patients there were 4 males and 3 females, with the median age of 37 (34, 51) years. Patients exhibited various clinical symptoms and signs depending on the tumor′s location. Four tumors were located in the cerebellum, 2 in the supratentorial region, and 1 in the spinal cord. Magnetic resonance imaging showed that 6 of the 7 patients had cystic and solid lesions, with focal or nodular enhancement and relatively unclear boundaries. Histopathological features had a diverse morphological spectrum and extensive grading. Five cases displayed a pilocytic astrocytoma-like appearance with infiltrative growth patterns, while two cases presented glioblastoma-like morphology, containing locally anaplastic pleomorphic xanthoastrocytoma with minor pilocytic components. All tumors were diffusely positive for GFAP and Olig2, while 4 tumors exhibited partial or complete loss of ATRX. The Ki-67 proliferation index ranged from 2% to 40%. Next-generation sequencing showed that tumor cells most commonly harbored MAPK pathway gene mutations, and/or homozygous deletions of CDKN2A/B, and/or ATRX mutations. Among the 7 HGAP models, 3 cases showed the three types of molecular genetic variations, 1 case showed MAPK mutations and homozygous deletions of CDKN2A/B, 1 case had MAPK mutations and ATRX mutations, 1 case had only MAPK mutations, and 1 case showed no detectable molecular changes. DNA methylation clustering analyses showed that the median model prediction score was 0.94 (range, 0.85-0.99) for the 7 HGAP models. Five cases showed the MGMT promoter hypermethylation. Four patients received radiotherapy and concomitant temozolomide treatment after surgery, while three patients received no known treatments. At the last follow-up, seven patients were alive without any tumor, two patients had recurrence, and one patient was alive with the tumor.Conclusions:HGAP is relatively rare and predominantly occurs in adults. It has a wide histopathological spectrum and various histological grades, characterized by piloid astrocytoma-like and glioblastoma-like histological features. Its diagnosis relies on methylation clustering analysis. Most tumors harbor gene alterations in the MAPK signaling pathway, along with homozygous deletions of CDKN2A/B or ATRX mutations. The biological behavior is typically aggressive, while imaging and histological findings can be misleading. Therefore, clinicians need to increase their diagnostic awareness of this tumor and prevent missed diagnoses.

Objective:To investigate the clinicopathological and molecular genetic features of high-grade astrocytomas with piloid features (HGAP).Methods:Clinical, histopathological and imaging data of 7 cases of HGAP diagnosed at the Neuropathology Center of Beijing Tiantan Hospital, Beijing, China from August 2023 to October 2024 were collected. The histopathological and molecular features for each case were analyzed.Results:Among the seven patients there were 4 males and 3 females, with the median age of 37 (34, 51) years. Patients exhibited various clinical symptoms and signs depending on the tumor′s location. Four tumors were located in the cerebellum, 2 in the supratentorial region, and 1 in the spinal cord. Magnetic resonance imaging showed that 6 of the 7 patients had cystic and solid lesions, with focal or nodular enhancement and relatively unclear boundaries. Histopathological features had a diverse morphological spectrum and extensive grading. Five cases displayed a pilocytic astrocytoma-like appearance with infiltrative growth patterns, while two cases presented glioblastoma-like morphology, containing locally anaplastic pleomorphic xanthoastrocytoma with minor pilocytic components. All tumors were diffusely positive for GFAP and Olig2, while 4 tumors exhibited partial or complete loss of ATRX. The Ki-67 proliferation index ranged from 2% to 40%. Next-generation sequencing showed that tumor cells most commonly harbored MAPK pathway gene mutations, and/or homozygous deletions of CDKN2A/B, and/or ATRX mutations. Among the 7 HGAP models, 3 cases showed the three types of molecular genetic variations, 1 case showed MAPK mutations and homozygous deletions of CDKN2A/B, 1 case had MAPK mutations and ATRX mutations, 1 case had only MAPK mutations, and 1 case showed no detectable molecular changes. DNA methylation clustering analyses showed that the median model prediction score was 0.94 (range, 0.85-0.99) for the 7 HGAP models. Five cases showed the MGMT promoter hypermethylation. Four patients received radiotherapy and concomitant temozolomide treatment after surgery, while three patients received no known treatments. At the last follow-up, seven patients were alive without any tumor, two patients had recurrence, and one patient was alive with the tumor.Conclusions:HGAP is relatively rare and predominantly occurs in adults. It has a wide histopathological spectrum and various histological grades, characterized by piloid astrocytoma-like and glioblastoma-like histological features. Its diagnosis relies on methylation clustering analysis. Most tumors harbor gene alterations in the MAPK signaling pathway, along with homozygous deletions of CDKN2A/B or ATRX mutations. The biological behavior is typically aggressive, while imaging and histological findings can be misleading. Therefore, clinicians need to increase their diagnostic awareness of this tumor and prevent missed diagnoses.