DENVER - A murine monoclonal antibody had very high sensitivity and specificity for melanomas with the V600E BRAF mutation, and exhibited perfect concordance between the primary and metastatic tumors in individual patients.
In addition to being a valuable screening tool, VE1 (anti-BRAF V600E) could be an extremely useful adjunct to DNA analysis, Michelle Vernali said at the annual meeting of the American Academy of Dermatology.
"I think that the sequential use of immunohistochemistry and molecular analysis will dramatically improve sensitivity and specificity for the detection of BRAF mutations, which is essential for the effective use of BRAF inhibitors," said Ms. Vernali, a fourth-year medical student at the University of North Carolina, Chapel Hill.
Michelle Vernali
According to Roche Diagnostics, the VE1 antibody has demonstrated 100% sensitivity and 99% specificity for BRAF mutations in colon cancer. In addition, it has shown high efficacy in detecting those mutations in thyroid cancer and hairy cell leukemia, and "shows promise" in non–small cell lung cancer and serous ovarian tumors.
According to the company, "The ... antibody has also been said to be a promising tool for patient stratification among individuals presenting with brain metastases."
Ms. Vernali and her colleagues examined the benefit of VE1 staining in 93 patients with metastatic melanoma. Of these, 76 had DNA pyrosequencing of either the primary (19) or metastatic lesion (57). Both primary and metastatic tumor samples were available for 17 patients.
Of the 76 patients with either primary or metastatic lesion samples, DNA pyrosequencing identified 26 that were positive for V600E and 40 that were negative. VE1 staining identified 22 positive samples and 44 negative samples, for a specificity of 100% and a sensitivity of 85%.
Sequencing also identified eight samples positive for V600K, and one each for V600R and V600Q. VE1 did not stain any of these samples.
Among the 17 patients with both primary and metastatic samples, VE1 was in 100% concordance with DNA sequencing, identifying three positive samples and 14 negative samples.
"There was little variability of strength or intensity of the staining, and very little intra-interpreter variance," Ms. Vernali said.
She proposed an algorithm for BRAF testing using VE1 with and without DNA sequencing.
· Insufficient tissue for initial DNA pyrosequencing:
– Stain with VE1.
– Identify BRAF V600E-positive or -negative patients.
· Sufficient tissue for DNA pyrosequencing:
– Stain with VE1.
– Stratify as VE1 positive or negative.
– If VE1 positive, conclude the patient is BRAF V600E positive.
– If VE1 negative, send sample for molecular sequencing to stratify into V600E positive, positive for another BRAF mutation, or BRAF negative.
This algorithm would identify V600E status in patients with tissue samples that would otherwise be insufficient for BRAF testing, she said. "If they had insufficient tissue for DNA sequencing, they could be stratified by immunohistochemistry and if positive, could be treated. Otherwise this is a population that now goes without BRAF-inhibiting therapy."
The algorithm is being tested in some sites already, she added, but needs additional validation before it can be broadly adopted.
Ms. Vernali had no financial disclosures.