Guardant told a federal judge that it believes Foundation Medicine and Personal Genome Diagnostics are coordinating to invalidate its patents.
The Patent Trial and Appeal Board has denied Foundation Medicine's request for Inter Partes review.
The broader market drove down the stock prices of many diagnostics companies. Natera, Guardant Health, and CareDx paced the gainers.
The firm plans to use the funds raised to support business activities, as it moves forward in the development of cancer early detection tests.
The company estimated that the offering could raise between $327.2 and $376.3 million, which it would use for various corporate purposes.
PGDx, the defendant in the liquid biopsy IP case, has alleged that Guardant's CEO should have been named as an inventor on patents but was purposefully left off.
During its earnings call this week, the liquid biopsy firm said it is planning a 10,000-patient trial to test its Lunar assay for colorectal cancer screening.
The liquid biopsy firm beat analyst estimates on the top and bottom lines and raised full-year revenue guidance to $145 to $150 million.
Overall, the share prices for 18 of the index's 27 companies fell month over month. Exact Sciences was the only firm whose share price improved in the double digits.
The investment bank gave the liquid biopsy company a price target of $90 and said that it views Guardant as the field leader.