Optic nerve assessment predicts retinoblastoma outcomes

By Sarah Guy, medwireNews Reporter

Magnetic resonance imaging (MRI) scans taken pre- and post-neoadjuvant chemotherapy (NACT) for International Retinoblastoma Staging System (IRSS) stage III retinoblastoma can indicate a patient's likely event-free and overall survival, indicate study results.

The prediction is based on the extent of optic nerve involvement, explain the researchers, with nerves staged based on their thickness, contrast enhancement, and length of involvement on MRI.

Specifically, the study showed that patients with optical nerve thickening at baseline and after NACT had significantly lower rates of event-free survival (EFS) and overall survival (OS) compared with those without optic nerve thickening.

"Metastasis to the CNS [central nervous system], the most common site for metastases, occurs via the optic nerve," write Sameer Bakhshi (All India Institute of Medical Sciences, New Delhi) and co-workers in the British Journal of Ophthalmology.

"Therefore, any staging systems or response assessment criteria in extraocular retinoblastoma need to provide a reliable prognosis based on the extent of optic nerve involvement, optic nerve thickening and contrast enhancement," they explain.

The team prospectively studied 28 untreated IRSS stage III retinoblastoma patients, aged a median of 3 years and cared for between May 2009 and June 2010. Patients underwent initial MRI scanning of the orbit and brain, and again after three cycles of NACT.

Patients were staged according to the system proposed by Bakhshi et al, taking into account optic nerve thickening (no/yes), optic nerve enhancement (no/yes), and optic nerve involvement area (intra-orbital <5 mm, intra-orbital ≥5 mm, intracanalicular, intracranial).

After an average follow up of 30.9 months, EFS and OS were 33.3% and 40.7%, respectively, and optic nerve thickening at baseline significantly predicted both outcomes. Indeed, just 7.1% and 14.3% of patients with such baseline thickening were event-free and alive, respectively, by the end of follow up.

A similar finding emerged for post-NACT MRI results. Specifically, optic nerve thickening after this treatment significantly predicted worse EFS and OS, with 0% and 10% of affected patients achieving these endpoints, respectively.

Intriguingly, note the authors, there was no significant difference in EFS and OS after NACT in patients with and without phthisis (bulky tumor) on MRI.

This finding suggests that a significant reduction in tumor bulk and a good clinical response - as defined by Response Evaluation Criteria in Solid Tumors, the current standard to radiologically assess response to treatment - does not necessarily correlate with better outcome.

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