Low-grade astrocytoma
Low-grade astrocytomas are slow-growing and rarely spread to other parts of the brain and spinal cord or other parts of the body.
Clasification
There are many types of low-grade astrocytomas. Low-grade astrocytomas can be either:
Low-grade astrocytomas are a subset of gliomas that originate from astrocytes. They are classified as WHO Grade 1 or 2, indicating slower growth and better prognosis compared to higher-grade astrocytomas.
WHO Classification
WHO Grade 1 Astrocytomas (Circumscribed Gliomas)
- Pilocytic astrocytoma (PA)
- Common in children and young adults
- Typically occurs in the cerebellum, hypothalamus, or optic pathway
- Associated with BRAF-KIAA1549 fusion
- Well-circumscribed, often cystic with a mural nodule
- Subependymal giant cell astrocytoma (SEGA)
- Associated with tuberous sclerosis complex (TSC1/TSC2 mutations)
- Typically arises near the foramen of Monro
- Can cause obstructive hydrocephalus
- Pleomorphic xanthoastrocytoma (PXA)
- Often in the temporal lobe, associated with seizures
- BRAF V600E mutation
- Angiocentric glioma
- Rare, slow-growing tumor associated with epilepsy
- Shows perivascular growth pattern
WHO Grade 2 Astrocytomas (Diffuse Gliomas)
- Diffuse astrocytoma, IDH-mutant
- IDH1 or IDH2 mutation present
- Lacks 1p/19q co-deletion
- Infiltrative, commonly in the cerebral hemispheres
- Diffuse astrocytoma, IDH-wildtype
- Worse prognosis compared to IDH-mutant forms
- May represent an early stage of glioblastoma
Molecular Classification & Diagnostic Markers
| Marker | Significance |
|---|---|
| IDH1/IDH2 mutation | Present in diffuse astrocytoma, WHO grade 2; confers better prognosis |
| ATRX loss | Suggests astrocytic lineage; seen in IDH-mutant astrocytomas |
| TP53 mutation | Common in IDH-mutant astrocytomas |
| BRAF fusion (KIAA1549-BRAF) | Seen in pilocytic astrocytoma |
| BRAF V600E mutation | Found in PXA and some diffuse gliomas |
| 1p/19q co-deletion | Suggests oligodendroglioma rather than astrocytoma |
| MGMT promoter methylation | Predicts response to temozolomide therapy |
Differential diagnosis
In a study, Geramizadeh et al. tried to evaluate IDH1 mutation and P53 mutation by immunohistochemistry as a simple and highly specific, and sensitive method to differentiate low-grade astrocytoma and reactive gliosis.
For 5 years (2013-2018), 50 cases of clinically documented reactive gliosis and 50 cases of low-grade astrocytoma were evaluated for the presence or absence of IDH1 and P53 mutation by immunohistochemistry.
Isocitrate dehydrogenase 1 was positive in 92% and 4% of the astrocytoma and reactive gliosis cases and P53 was positive in 90% and 4% of the cases with the final diagnosis of astrocytoma and reactive gliosis, respectively.
The combination of P53 and IDH1 as an immunohistochemical panel showed a specificity of 96% and sensitivity of 91% for differential diagnosis of reactive gliosis and low-grade astrocytoma. These 2 markers can be extremely helpful for this differential diagnosis 1).
mIDH1R132H is a tumor-specific marker that is superior to other established markers to differentiate reactive from neoplastic cells in grade II and III gliomas and allows identifying tumor cells in posttherapy specimens with extensive reactive changes. As IDH mutations are not characteristic of grade IV primary glioblastomas, this antibody cannot differentiate primary glioblastoma from reactive gliosis. Thus, caution has to be taken and a combined panel with other markers is needed 2).
Case series
Laws et al., conducted a retrospective review of surgically treated, histologically proven cases of low-grade (Grade 1 or 2) astrocytomas. Follow-up analysis, with survival time as the end-point, was completed using multivariant statistical analysis. In the 461 cases of supratentorial low grade astrocytoma in this study, age of the patient at the time of surgery was by far the most important variable in predicting length of survival. Other variables correlating with increasing survival times were: gross total surgical removal, lack of major preoperative neurological deficit, long duration of symptoms prior to surgery, seizures as a presenting symptom, lack of major postoperative neurological deficit, and surgery performed in recent decades. The multi-variant regression analysis showed that radiation therapy was of clear benefit, primarily in older patients with incompletely removed tumors. For purposes of establishing prognosis and testing the results, a “score” was developed to predict survival times, based on the most important variables. The data in this study provide a basis for the analysis of future modes of management of low-grade gliomas 3).