C-MYC Expression In Newly Diagnosed Multiple Myeloma

Overexpression of the c-MYC proto-oncogene plays an important role in the malignant phenotype of Burkitt lymphoma and diffuse large B cell lymphoma, but its role in multiple myeloma (MM) is controversial. Dysregulation of c-MYC, which is highly prevalent in human MM cell lines, is classically described as a late progression event. Translocations involving the c-MYC locus are reported to be present in approximately 13 % of newly diagnosed MM patients. However, a recent study showed expression of a MYC activation signature in 67 % of MM, and found c-MYC expression in 60 % of patients by immunohistochemistry (IHC). It has been suggested, that c-MYC expression is associated with the transition from monoclonal gammopathy of undetermined significance (MGUS) to MM, as an early event of MM pathogenesis, and that such a MYC addiction might have a useful therapeutic potential. However, the prevalence and the clinical associations of c-MYC expression among newly diagnosed MM patients need further assessment.

We conducted a retrospective IHC study to evaluate the prevalence of c-MYC expression in newly diagnosed MM. Secondly, we wanted to assess, whether c-MYC expression was associated with factors known to influence prognosis, such as the patient’s clinical and laboratory features, end organ damage, International staging system (ISS) stage, and response to primary treatment. Thirdly, we wanted to assess, whether c-MYC expression was associated with known immunophenotypic variables in MM, such as CD20, Pax-5, Cyclin D1, and CD56.

Bone marrow aspirates from 119 patients diagnosed with MM from 2005-2010 were examined retrospectively. Tissue microarrays (TMAs) were constructed from formalin fixed, paraffin embedded samples using four 1mm cores from each patient sample. IHC was carried out with commercially available antibodies. Plasma cells were identified with anti-CD138 IHC. For detection of c-MYC, we used an anti-c-MYC rabbit monoclonal antibody obtained from Epitomics (Clone EP121). Samples were evaluated as c-MYC-positive, if at least 30 % of tumour cell nuclei were stained. Clinical data were obtained from the Danish Multiple Myeloma Database. Patients who received primary treatment (n=96) were examined separately based on whether they were treated with high-dose therapy (HDT) (n=31) or other treatment regimens (n=65). Response rates to primary treatment were evaluated. Associations between variables were assessed by calculating Fisher’s exact tests.

The TMAs yielded sufficient material for assessment of c-MYC expression in 87 % of the study population. c-MYC expression was found in 44 (43 %) patients. At the time of diagnosis, c-MYC expression was significantly associated with the presence of extra-medullary myeloma (p = 0.026) and higher than the mean (36.6 %) bone marrow infiltration (p = 0.005). There were trends for c-MYC-positive patients to have World Health Organization (WHO) performance status 2 (p = 0.071) and hypercalcemia (p = 0.086). c-MYC expression was not associated with ISS stage, anemia, renal insufficiency or the evidence of bone disease. Among the patients who were not eligible for HDT, c-MYC expression had a trend to preclude achievement of complete response (CR) after primary treatment (p = 0.061). Only 5 patients achieved CR in this group, and all were c-MYC-negative. Such a trend was not found among patients who were treated with HDT, where c-MYC expression was not associated with specific response rates. Expression of CD20, Pax-5, Cyclin D1, and CD56 were found in 16 %, 38 %, 43 %, and 73 % of patients, respectively. c-MYC expression was not associated with any of the assessed immunophenotypic variables.

c-MYC expression was found in almost half of newly diagnosed MM patients, which supports the theory that c-MYC activation is an early event in MM pathogenesis. c-MYC expression was associated with extra-medullary myeloma and high bone marrow infiltration, both factors known to have a negative effect on prognosis. Patient survival could not be evaluated in this cohort due to limited observation periods, but the results suggest that c-MYC expression should be studied further in patient cohorts with longer observation periods. Also, the mechanisms behind c-MYC expression should be addressed in future studies. c-MYC expression was not associated with the expression of CD20, Pax-5, Cyclin D1, or CD56.

No relevant conflicts of interest to declare.