Pediatric Medulloblastoma Treatment & Management

Following upfront maximal safe surgical resection, standard of care approach for medulloblastoma is dependent on risk stratification and generally consists of chemotherapy and radiotherapy. New treatment approaches are being developed in an attempt to reduce long-term toxicity of therapy and include reduction of the total dose or volume of radiotherapy, use of less neurotoxic chemotherapeutic agents and newer targeted therapeutic agents, and use of high dose chemotherapy with autologous stem cell rescue in lieu of craniospinal irradiation (CSI).

Although there is insufficient evidence to routinely recommend the use of proton therapy, for younger children with medulloblastoma, strong consideration should be given for proton-beam radiotherapy when available.  Compared to conventional radiotherapy, proton-beam therapy provides similar efficacy but offers the advantage of minimizing the risk of long term side effects including but not limited to ototoxicity, cardiopulmonary toxicity and secondary malignancies. ^[5]

Studies that incorporate molecular profiling to guide adjuvant therapy are underway.

Radiation therapy

Radiation strategies can be divided into local control and treatment of micrometastatic disease with craniospinal irradiation.  Historically, the entirety of the cerebellum (posterior fossa) was radiated.  Increasingly, the approach of more precise targeting of the tumor bed with an appropriate margin is being done.

Average-risk disease

The current recommendation is 23.4 Gy to the craniospinal axis, followed by a boost of 30.6 Gy to the primary tumor site.  In general, start of radiation should be timed for no later than 4 weeks from surgery to maximize clinical outcomes.

Reducing the amount of craniospinal radiation in an attempt to decrease morbidity without jeopardizing survival appears to be successful in this group. In a report by the International Society of Pediatric Oncology, children with average-risk medulloblastoma randomly received either the standard 36 Gy or a reduced dose of 24 Gy to the neuraxis. ^[6] It was found that no statistical difference in progression-free survival rates was demonstrated between the groups as long as the initiation of radiotherapy was not delayed by the administration of chemotherapy before radiation.

In the largest trial conducted for average-risk medulloblastoma by the Children's Oncology Group (COG), survival rates following reduced radiation therapy boost volumes were comparable to standard treatment volumes for the primary tumor site but lower CSI doses were associated with higher relapse rates and worse survival outcomes.  In this study, patients less than 8 years of age were randomized to receive 18 Gy vs. 23.4 Gy whereas all patients were randomized to either local boost versus radiation to the entire posterior fossa. ^[7]

Studies to determine the feasibility of avoiding radiation therapy altogether in WNT-activated medulloblastoma, a subgroup with excellent prognosis, are ongoing.

High-risk disease

The current recommendation is 36 Gy to the craniospinal axis, followed by a boost of 19.8 Gy to the primary tumor site and an additional 19.8 Gy to focal metastatic sites. In general, start of radiation should be timed for no later than 4 weeks from surgery to maximize clinical outcomes.

Infants (< 3 years of age)

Radiation therapy for patients younger than 3 years, the poorest risk group, is generally avoided because of its deleterious effects on intellectual development especially in this age group.  Previous attempts to decrease CSI dose and maintain outcomes in this age group were unsuccessful.  In lieu of this, in an effort to delay or omit radiation, current protocols utilize high dose chemotherapy approaches.

Relapse/Recurrence

There remains no standard approach in the treatment of relapsed medulloblastoma. The prognosis for relapsed medulloblastoma is dismal, especially in those who have previously received radiation. Treatment approach is primarily based on whether the child has had craniospinal radiation as part of initial therapy. Re-irradiation is often not performed due to concerns surrounding cumulative CNS toxicity and unknown efficacy.  If a patient has had prior craniospinal radiation, a small boost of radiation can still be considered.

Chemotherapy

Cytotoxic chemotherapy may be used in the initial treatment (in infants), as maintenance therapy (for average and high-risk disease) or for disease recurrence. In patients less than 3 years of age, incorporation of high dose chemotherapy strategies may delay or obviate the need for radiation therapy.

To date, there exists only a handful of open clinical trials that incorporate molecular risk stratification to help guide therapy.

Average-risk disease

Standard therapy post-radiation is with the use of cisplatin-based regimens. Many contemporary chemotherapy protocols use a combination of cisplatin, vincristine, lomustine (CCNU) and cyclophosphamide as maintenance therapy for approximately one year following radiation therapy.

Group 2/SHH-activated medulloblastomas are characterized by mutations in smoothened SMO, which is upstream of SHH.  Vismodegib, an SMO inhibitor, has promising efficacy in patients who harbor upstream SHH-pathway mutations (ie, SMO and PTCH1 mutations)

High-risk disease

As in average risk medulloblastoma, following induction therapy with radiation therapy, the most effective chemotherapy agents utilized are cisplatin, vincristine, lomustine (CCNU) and cyclophosphamide.  The use of daily carboplatin (in addition to weekly vincristine) as a radiosensitizing agent is currently being studied in high risk medulloblastoma.

Risk adapted radiotherapy followed by a shortened schedule of four consecutive high dose cyclophosphamide-based chemotherapy with autologous stem cell rescue has been shown to improve outcome of patients with high risk medulloblastoma. ^[8]  

Group 3 and 4 patients generally fare poorer than group 1/WNT and group 2/SHH cases. As such, St. Jude is investigating the addition of gemcitabine, a pyrimidine nucleoside analogue, and pemetrexed, a folate antimetabolite, to group 3 and 4 medulloblastoma patients based on promising pre-clinical data. ^[9]

Infants

Intensive chemotherapy with stem cell support has shown promise in recurrent and infant medulloblastoma cases. Dose intensive chemotherapy strategies incorporate up to five cycles of high dose methotrexate-based regimens followed by high dose chemotherapy (up to three courses using carboplatin, thiotepa with or without etoposide) with autologous stem cell rescue. Stem cells are typically harvested following the first cycle of induction chemotherapy and frozen for later use. 

Recurrence

There is no standard chemotherapy approach for relapsed medulloblastoma. Overall outcomes are poor and median overall survival following relapse is less than one year. The combination of bevacizumab and irinotecan, with or without temozolomide, can produce objective responses with minimal toxicity in recurrent medulloblastoma cases. High dose chemotherapy with autologous stem cell rescue has shown potential benefit in patients who are able to achieve minimal residual disease following salvage chemotherapy but carry significant morbidity. Alternatively, metronomic chemotherapy, an approach where low daily doses of drug are used to reduce tumor angiogenesis and promote cancer apoptosis, with or without the addition of intrathecal chemotherapy, has also shown promise with few reports of long term survivors.

The goal of surgery is to resect as much of the tumor as safely as possible and to reduce the pressure inside the brain caused by blockage of cerebrospinal fluid (CSF) outflow.

Suboccipital craniotomy

Because the tumor is often friable, gentle suction is used. Microdissection is then used to remove adherent portions. Modern neurosurgical techniques permit complete or near-complete resection with little or no significant increase in morbidity and mortality rates compared with more conservative surgery.

Because surgical estimates of the extent of resection may not be reliable, postoperative MRI evaluation for residual disease is required within 72 hours of surgery the procedure.

As many as 40% of patients have some degree of new neurologic dysfunction postoperatively. One ill-defined syndrome is posterior fossa syndrome, characterized by mutism, cerebellar dysfunction, supranuclear cranial nerve palsy, and hemiparesis that occurs 12-48 hours after surgery. Symptoms generally resolve within weeks to months from surgery with the help of speech, occupational and physical therapy. However, as many as 50% of patients can experience long-term residual deficits.

Ventriculoperitoneal shunt

Treatment of hydrocephalus is almost always needed in medulloblastoma patients. Approximately 50% of cases require placement of a ventriculoperitoneal shunt at the time of operation (or shortly thereafter) because of unresolving obstructive hydrocephaly. Alternatively, endoscopic third ventriculostomy is increasingly used to avoid the placement of a permanent ventricular shunt; this approach can be successful in as much as a third of patients.

Central venous catheter placement

Surgically placed catheter inserted into a large deep vein and used to obtain blood tests and administer chemotherapy.  Generally, an implanted port is placed on one side of the chest.  In younger patients or those requiring high dose chemotherapy and autologous stem cell transplantation, a tunneled Broviac line may be placed instead.

Ommaya reservoir

Some infant brain tumor protocols combine systemic chemotherapy with intrathecal/intraventricular chemotherapy. Placement of an Ommaya reservoir facilitates repetitive administration of drugs into the CSF and ensures more reliable drug delivery and distribution.

In North America, intraventricular administration of chemotherapy requiring Ommaya placement is primarily restricted to salvage protocols in relapsed cases.

As a direct result of the tumor and/or therapy, many patients are referred to occupational, physical, hearing, and speech therapists for rehabilitation of common neurologic dysfunction. Neuro-ophthalmologists may also be consulted after successful treatment to evaluate persistent gaze palsies that may affect visual development.

Team members for the care of all patients should include specialists from each of the following:

• Neurosurgery

• Pediatric oncology (Neuro-oncology when available)

• Radiation oncology

• Neuroradiology

• Neurology

• Psychology

• Endocrinology

• Rehab Medicine

• Ophthalmology (Neuro-ophthalmology when available)

Diet

No specific dietary restrictions or requirements are indicated.

Patients who develop severe anorexia or weight loss as a result of therapy may need supplemental nutrition to maintain daily requirements. Most patients can tolerate enteral supplementation, but may require nasogastric/nasojejunal (NG/NJ) tube placement while some may need parenteral support.  Less commonly, surgery may be needed for gastrostomy tube (G-tube) placement.

Activity

Most patients have no restrictions on activity other than limitations from neurologic deficits caused by the tumor and treatment.

Patients with central lines and/or ventriculoperitoneal shunts may be restricted from performing high-impact sports (eg, diving, wrestling).

School performance needs to be carefully monitored and depending on limitations from neurologic deficits, may require added support at school.