High-throughput sequencing and other molecular studies
Three molecular study options are available for the diagnosis of MF: TCR/PCR, which is the traditional clonality study; next-generation high-throughput DNA sequencing; and flow cytometry.
A TCR/PCR study showing a monoclonal T-cell clone on a more subdued polyclonal background is highly suggestive of MF, as opposed to other inflammatory dermatoses. Early in the disease, however, the pattern can be oligoclonal, an inconclusive result. This point is where taking multiple biopsies from different skin sites becomes extremely helpful to amplify TCR/PCR’s sensitivity and specificity. Indeed, investigators at Stanford (Calif.) University have reported that TCR/PCR analysis showing an identical T-cell clone in biopsy specimens from two different skin sites had 82.6% sensitivity and 95.7% specificity for unequivocal MF.
High-throughput sequencing of the T-cell receptor gene has greater specificity for diagnosis of MF than TCR/PCR, and with similar sensitivity.
“The sensitivity of high-throughput sequencing is okay, but really we want it to be helpful in those wishy washy cases where we get an oligoclonal result on TCR/PCR; that’s, I think, an ideal use for it,” Dr. Shinohara said.
In addition to its role in establishing the diagnosis of MF, high-throughput sequencing shows promise for two other potential applications: detection of residual disease following stem cell transplantation and risk stratification in patients with early-stage disease.
Citing a landmark Stanford retrospective cohort analysis of actuarial disease-specific survival in 525 patients with MF and Sezary syndrome, she noted that the majority of patients had stage IA or IB disease – meaning patches and/or plaques on less than or more than 10% of their body surface area – and the survival curves of these patients with early-stage CTCL were flat.
“Most patients are going to live for decades with their disease if they have early disease, and that’s very reassuring for patients,” the dermatopathologist observed.
And yet, early-stage disease does not follow an indolent lifelong course in a subset of patients; rather, their disease becomes aggressive and resistant to all treatments short of stem cell transplantation. Investigators at Harvard University, Boston, have reported that high-throughput sequencing of the T-cell receptor beta gene in lesional skin biopsies is a powerful tool for early identification of this high-risk subpopulation of patients with early-stage MF. They demonstrated in a cohort of 141 patients with early-stage MF, then again in a validation cohort of 69 others, that a tumor clone frequency (TCF) greater than 25% in lesional skin, as measured by high-throughput sequencing, was a more powerful predictor of disease progression than any of the established prognostic factors.
In the discovery set, a TCF in excess of 25% was associated with a 4.9-fold increased likelihood of reduced progression-free survival; in the validation set, the risk was 10-fold greater than in patients with a lesser TCF. These were significantly greater risks than those seen with other proposed biomarkers of diminished progression-free survival, including the presence of plaques; stage IB, as opposed to IA, disease; large-cell transformation; age greater than 60 years; and elevated lactate dehydrogenase levels.
Although this groundbreaking work requires confirmation in another dataset, “this may be something we evolve towards doing in patients with early disease to pick out those who may have bad outcomes later,” Dr. Shinohara commented.
Still, she stressed, molecular studies will never replace histopathologic analysis for diagnosis of MF. “Judicious use of molecular studies may help in establishing the diagnosis, but I don’t think any one molecular study is ever going to be our home run,” she said.
She reported no financial conflicts regarding her presentation.
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