Oct. 31, 2015
A multidisciplinary team from the departments of Ophthalmology, Molecular Medicine, and Laboratory Medicine and Pathology at Mayo Clinic's campus in Rochester, Minnesota, has studied three patients with known diffuse large B-cell lymphoma to determine whether an MYD88 L265P mutation was present in any case of definite vitreoretinal diffuse large B-cell lymphoma.
An L265P (T-C at position 38182641 at 3p22.2) mutation of MYD88, a protein associated with the innate immune system, is present in many cases of Waldenstrom's macroglobulinemia. The mutation, which causes a constitutive activation of the MYD88 protein and triggers NF-kappaB signaling, has become a diagnostic criterion for Waldenstrom's macroglobulinemia.
The same MYD88 L265P mutation occurs in about 15 percent of cases of systemic diffuse large B-cell lymphoma. The most common form of vitreoretinal lymphoma is the diffuse large B-cell form.
"No one has shown whether this mutation occurs in vitreoretinal lymphoma, which is a rare form of central nervous system diffuse large B-cell lymphoma," says Jose S. Pulido, M.D., Ophthalmology, at Mayo Clinic in Rochester, Minnesota. Results of the team's research were published in Retina in April 2015.
Mutation identified in 2 of 3 subjects
The Mayo team found three patients with classic clinical findings of vitreoretinal lymphoma and histologic confirmation — and enough tissue to evaluate for the mutation. The MYD88 mutation assay required a minimum input of 5 ng of DNA.
"Clinically and histologically, there did not seem to be differences in the three cases; all were severe," says Dr. Pulido. "The ages were similar in all three cases, and all started as vitreoretinal lymphoma. All three had vitreous involvement. Two had subretinal involvement, one who was positive and one who was negative for the MYD88 mutation. All had diffuse large B-cell lymphoma noted histologically. Extraocular involvement occurred in all three cases, but systemic involvement was seen in the negative L265P case, and central nervous system involvement was seen in the positive L265P cases."
The research team evaluated the formalin-fixed paraffin-embedded cells from the patients using a validated amplification-refractory mutation system polymerase chain reaction, which results in a normal product of 141 base pairs and a mutation amplicon of 72 base pairs (each plus or minus 5 base pair resolution by capillary electrophoresis), to determine the presence of the mutation.
The polymerase chain reaction product quality was determined from mean relative fluorescence unit values, requiring greater than a 0.1 relative fluorescence unit if the mutant product was detected and a relative fluorescence unit of 0.5 or greater for a negative (wild-type) product.
Researchers validated the test on 54 samples that had either small B-cell lymphoma or Waldenstrom's macroglobulinemia. A sensitivity of 1 percent mutant allele in a wild-type population could be detected. The test had a 92 percent clinical sensitivity and a 92 percent specificity.
Further studies required
"Our study confirms that MYD88 L265P constitutive activating mutations are present in at least some cases of the diffuse large B-cell lymphoma form of vitreoretinal lymphoma," says Dr. Pulido. "The 74 ± 2 base pair product seen from the mutated MYD88 protein was noted in two of the three cases." The finding is significant for two reasons:
- It helps in making the difficult diagnosis of vitreoretinal lymphoma by providing another marker that may help with diagnosis of the disease.
- There are now specific inhibitors of the MYD88 L265P mutation, as noted by Steven P. Treon, M.D., Ph.D., and others in Hematology/Oncology Clinics of North America in 2014.
"The limitations of this study are that we only used definite cases of vitreoretinal lymphoma," says Dr. Pulido. "We cannot determine the efficacy of this test in people whose diagnosis from the histologic examination was negative. Further studies are required to determine the lower level of sensitivity in these cases.
"Also, we were only interested in seeing whether any of our cases would test positive, so further studies are required to determine the exact incidence of this mutation in cases of diffuse large B-cell form of vitreoretinal lymphoma."
For more information
Pulido JS, et al. MYD88 L265P mutations are present in some cases of vitreoretinal lymphoma. Retina. 2015;35:624.
Treon SP, et al. Waldenstrom macroglobulinemia. Hematology/Oncology Clinics of North America. 2014;28:945.