Pilocytic astrocytoma

Hui-Kuo G. Shu, MD, PhD
Last Modified: September 29, 2002

Dear OncoLink "Ask The Experts,"

My 20-month-old son was recently diagnosed with a pilocytic astrocytoma attached to his brain stem. The tumor was explained to me as being mildly malignant with a possibility of becoming more aggressive. During his surgery 2/3 of the tumor was removed. My question is; of the remaining tumor, are there any studies that show the percentage of this astrocytoma becoming more aggressive (more malignant)?

Hui-Kuo G. Shu, MD, PhD, Assistant Professor in the Department of Radiation Oncology at the University of Pennsylvania, responds:

Your son has a pilocytic astrocytoma that had a significant portion resected (surgically removed). Pilocytic astrocytomas are considered the lowest grade astrocytomas (least aggressive). They tend to be well-circumscribed and, depending on the location, can often be completely resected (which is generally considered to be curative). However, some locations, such as in the brainstem, are more difficult to resect completely because of potential morbidity associated with a highly aggressive surgical approach. In this situation where a subtotal resection is performed, a significant risk of tumor progression exists. If there were a recurrence, the great majority of these would continue to be pilocytic at recurrence. However, as your son's physicians have correctly informed you, the possibility exists for malignant transformation at progression. The probability of this occurring is very low with an estimated incidence of 0.9% based on a study of 107 patients with cerebellar pilocytic astrocytoma by a group at the Mayo Clinic (Tomlinson et al., J Child Neurol 9:301-10, 1994). Therefore, while malignant transformation can happen, it is very rare.