Retinoblastoma is a rare form of eye cancer that primarily affects young children, typically before the age of five, with an average diagnosis around 18 months. This condition involves the retina, the light-sensitive tissue at the back of the eye. Early detection is important for successful treatment and preservation of vision.
Recognizing Potential Signs
The most common sign of retinoblastoma is leukocoria, often described as a “cat’s eye reflex,” where the pupil appears white or pale instead of the normal red reflection when light, such as a camera flash, shines into the eye. This white appearance occurs because the tumor reflects the light. Parents or caregivers often notice this symptom first, sometimes in photographs.
Other signs may also indicate the presence of retinoblastoma. These can include strabismus, a new squint or misalignment of the eyes, where one eye may turn inward or outward. A child might experience redness, swelling, or pain in the eye, or notice a difference in the size of their eyes, with one appearing larger than usual. In rare instances, there might be a change in the iris color of one eye.
Medical Evaluation and Imaging
If retinoblastoma is suspected, a pediatric ophthalmologist will perform a thorough eye examination. A comprehensive eye exam under anesthesia (EUA) is typically the primary diagnostic tool for retinoblastoma, especially for children between 2 months and 5 years old. This procedure, performed in an operating room while the child is asleep, allows the ophthalmologist to fully visualize the retina using an indirect ophthalmoscope and sometimes a Retcam, which projects high-resolution images onto a screen.
Various imaging techniques are used to assess the tumor’s extent and spread. Ocular ultrasound (B-scan) is a common and safe method, using sound waves to image the eye, identify calcifications, and measure its size. Magnetic Resonance Imaging (MRI) of the brain and orbits is an important tool, providing detailed images to evaluate tumor infiltration of the optic nerve, extraocular extension, and the possibility of other brain tumors, such as pineoblastoma. While Computed Tomography (CT) scans can detect calcifications, they are generally avoided in children due to radiation exposure, as MRI is often equally effective and does not involve ionizing radiation.
Pathology and Genetic Confirmation
Definitive confirmation of retinoblastoma and its genetic basis involve specific tests. A biopsy of the eye tumor is generally not performed due to the risk of spreading cancer cells. Pathological examination of tissue is usually conducted if the entire eye is removed as part of treatment, allowing for microscopic confirmation of cancer cells.
Genetic testing plays a significant role in understanding retinoblastoma, identifying mutations in the RB1 gene, which is responsible for producing a tumor suppressor protein. This testing can be performed on tumor tissue or on a blood sample. Identifying an RB1 mutation in the blood confirms hereditary retinoblastoma, meaning the mutation is present in all cells of the body and can be passed down to offspring. Approximately 39-50% of retinoblastoma cases are due to a germline mutation, while about 60% are spontaneous or non-hereditary, typically affecting one eye. Genetic testing helps determine if the condition is hereditary, which has implications for family screening and assessing the risk of other cancers later in life for the child and potential risk for future children.
Understanding the Diagnosis
Upon diagnosis, retinoblastoma is classified based on whether it affects one eye (unilateral) or both eyes (bilateral). Unilateral retinoblastoma accounts for approximately two-thirds of cases and is often diagnosed later, between ages two and three years, while bilateral cases are more commonly diagnosed before a child’s first birthday. Bilateral retinoblastoma is almost always hereditary, whereas about 13-19% of unilateral cases also carry a germline mutation.
The diagnosis also involves staging, which describes how far the cancer has spread and helps predict outcomes and guide treatment decisions. Retinoblastoma is broadly classified as intraocular, meaning the cancer is confined within the eye, or extraocular, indicating it has spread outside the eye. Staging systems, such as the International Classification for Intraocular Retinoblastoma (Groups A through E) or the AJCC staging system, consider factors like tumor size and location within the eye, and if there is any spread to the optic nerve or beyond. A multidisciplinary team of specialists, including ophthalmologists, oncologists, geneticists, and radiologists, collaborates to interpret these diagnostic findings and develop a comprehensive understanding of the child’s specific condition.