Leading the gainers in the 360 Index was GenMark, whose stock price was up 30 percent last month. Invitae led the decliners as its share price fell 24 percent.
The company is taking the step to continue listing its shares on the Nasdaq, which had warned OpGen that did not meet a listing requirement calling for a minimum bid price of $1 per share.
Investors in Exact Sciences went on a selling spree after CellMax publicized data suggesting its test could outperform Cologuard for the early detection of colorectal cancer.
The company's stock faced delisting for trading below $1 for 30 consecutive business days in violation of the Nasdaq's requirements.
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.
OpGen had previously been warned by Nasdaq that it failed to meet listing requirements. Last week, the firm was told that it was ineligible for an extension to regain compliance.
Paced by Accelerate Diagnostics and Bio-Rad, the 360Dx Index beat the broader markets. Shares of GenMark and Opko, however, were sharply down.
Last month, the company was notified that it no longer met the Nasdaq's stockholder equity listing requirement and faced delisting.
Earlier this year, Rosetta effected a 1-for-12 reverse stock split after failing to meet the Nasdaq's $1 minimum bid price requirement.
The firm had been notified by the exchange in August that it failed to meet a listing requirement calling for a minimum $1 bid price on its stock.