Treatment for retinoblastoma
RB treatment is based on two main principles: first to save the patient’s life and second to preserve the patient’s vision.
The multiple modalities of treatment include surgery, chemotherapy, radiation therapy and topical therapies (thermotherapy, cryotherapy, photocoagulation and brachytherapy). Treatment may include one or more of these modalities that can be administered simultaneously or not, always honouring the two main treatment principles described above.
Surgery: Enucleation is a surgical procedure done under anaesthesia and performed by an experienced ophthalmologist that consists of the removal of one or both eyes from the orbits. Enucleation is reserved for those patients whose eye/s are extensively compromised by the tumour and cases when, because of the damage inflicted by the tumour, it is unlikely that any vision can be restored. Immediately after enucleation, an orbital implant will be placed inside the orbit and eventually replaced by a prosthetic eye. A pathologist will look at the eye under the microscope to determine if the tumour extended beyond the limits of the eye and the optic nerve. Subsequent treatment, if a treatment is required, will be based on the pathology results. Enucleation is still the treatment of choice for most cases with unilateral retinoblastoma.
Chemotherapy: Chemotherapy consists of multiple medications that are effective for killing RB cells. Those medications are also toxic and can cause many short-term and long-term side effects that should be explained by an oncologist. Chemotherapy is used in every situation when there is a chance of preserving the vision, to avoid enucleation and radiation therapy, and also in situations when the disease has spread outside of the eye. Chemotherapy can be administrated in different ways:
- Systemic chemotherapy: In this case, medication/s are administered through the patient’s vein. Based on the medication toxicity profile and schedule, chemotherapy can be given as outpatient or inpatient. Patients generally experience mild to severe systemic side effects after chemotherapy. However, most of those side effect can be effectively controlled and ameliorated with other medications and interventions. Systemic chemotherapy is occasionally needed in cases where there are risk factors in the pathology examination of the enucleated eye in order to reduce the risk of metastatic relapse.
- Intra-arterial chemotherapy: Chemotherapy is administrated through a catheter that is positioned in the ophthalmic artery, so the medication is delivered directly to the eye. This procedure is done under anaesthesia and consists on the placement of a catheter in an artery in the groin area that is then moved up inside the arterial system until reaching the ophthalmic artery, the artery that flows to the eye. Chemotherapy is then delivered inside this artery, avoiding most of the side effects of systemic administration. This procedure can only be done in children that are more than 6 Kg and older than 6 months.
- Intravitreal chemotherapy: This is a procedure that consists of the application of chemotherapy directly inside the eye (inside the vitreous humour). This procedure is reserved for tumours that have spread inside the vitreous humour and either did not respond or recurred after other treatment modalities. An ophthalmologist administers this kind of chemotherapy under anaesthesia.
Radiation therapy: RB is a radiosensitive tumour and responds very well to this kind of treatment. In the past decades, radiation therapy was the only treatment modality that allowed eye preservation, until chemotherapy was introduced. However, multiple studies around the world have shown an association between radiation therapy and the development of new types of cancer later in life, especially in RB survivors with bilateral RB9-11. For this reason, external beam radiation therapy is avoided nowadays unless it is absolutely necessary, and chemotherapy or local therapies are preferred.
There are two main forms in which radiation therapy can be administrated to patients with RB:
- External beam radiotherapy (EBRT): Radiation is given through a linear accelerator, which is a machine similar to the one used to do CT scans. Radiation is given daily and for several weeks. Most patients have to be sedated for treatments unless they are old enough to stay still during the procedure.
- Brachytherapy: A radiation seed is placed over the tumour and sewn into the sclera to keep in place under anaesthesia. The seed is left in there for a couple of days and it will provide radiation directly to the tumour. This radiation modality has not been associated with secondary cancers.
Local therapies: There are multiple local therapies that the ophthalmologist can use to reduce the tumour size when the tumour is not too big. They deliver different kinds of energy (heat, cold, laser, radiation) directly to the tumour and they can be used alone or in conjunction with other treatment modalities. These therapies include thermotherapy, cryotherapy, photocoagulation and brachytherapy.