The investment firm also reduced its price target to $30 per share from $37 citing "lower overall conviction" that Myriad would meet its revenue projections.
The investment bank downgraded LabCorp's shares to a Hold rating from Buy and lowered the target price on the stock to $162 from $195.
The investment bank cited disappointing first quarter financial results, a slow uptake to the business, and competitive pressures for the downgrade.
Despite the downgrade, the investment bank described NeoGenomics as "well-positioned" to grow its customer base in multiple customer segments.
The 360Dx Index was down 3 percent in February, reflecting similar losses in the broader markets. GenMark Diagnostics and Opko Health were the biggest decliners.
Several firms, such as Exact Sciences and Foundation Medicine, saw their share values more than double during the year, while NantHealth and GenMark saw their share values shrink.
The stock prices of 17 of the 25 firms in the 360Dx Index fell month over month with Enzo Biochem and Bio-Rad leading decliners.
The investment bank previously had a Neutral rating for the company, and it lowered the price target on Genomic Health's stock to $25 from $28.
In a note, Cowen analyst Doug Schenkel said the company has had trouble meeting its targets and suggested it pursue a strategic sale of its nCounter platform.
September was the third consecutive month in which the index barely moved month over month. NantHealth paced the gainers, while Quest Diagnostics paced the decliners.