Check out the companies making headlines midday Monday:

Alphabet, Facebook — Alphabet shares tanked more than 6% after news that the Justice Department was preparing an antitrust lawsuit against Google. According to reports, the probe would look into Google's search practices and other businesses. Facebook shares also fell 7.5% amid worries of the broader tech sector falling under greater government scrutiny.

Amgen, Mirati Therapeutics — Shares of biotech company Amgen jumped 3.4% after results from a cancer study examining Amgen's gene therapy drug showed significant reduction in the size of tumors in patients with advanced lung cancer. Promising results also drove shares of Mirati up 31.6% as the biotech company is also developing a drug that targets the same gene mutation.

DuPont — Shares of DuPont jumped 17.8% after a Morgan Stanley analyst initiated coverage of the chemical company with an overweight rating. The analyst said it sees value in DuPont regardless of whether it becomes a "true multi-industry" company or keeps its businesses separated.

Teva Pharmaceutical Industries — An analyst at Oppenheimer upgraded Teva to outperform from perform, citing improving fundamentals and "in line" execution from management. The stock rose 2.9%.

Waste Management —Shares of Waste Management climbed more than 1.9% after an RBC Capital Markets analyst upgraded the stock to outperform from market perform. "We see Waste Management delivering out-sized earnings growth, driven by sustained organic growth rates," the analyst said in a note.

Cypress Semiconductor — Cypress Semiconductor surged more than 23.9% on news that German company Infineon will buy the chip-maker for $23.85 per share. The sale values Cypress at $10.06 billion. Infineon's share price fell 7.1% Monday on the news.

Humana — Shares of Humana gained 1.2% after an SEC filing revealed that the company is not interested in merging with health insurer Centene. This deal would have diverged from Centene's plans to acquire WellCare Health Plans. Centene shares dropped more than 9%.

Nektar Therapeutics — The biotechnology stock rose jumped 8.8% after the company released positive trial results for bempegaldesleukin, a drug that aims to boost a cancer patient's immune system.

Advanced Micro Devices — Advanced Micro Devices gained 0.6% after the chipmaker announced a multi-year deal with Samsung to license its custom graphics intellectual property for use in its mobile devices. Samsung will be paying AMD license fees and royalties.

Boeing — Shares of aircraft-maker Boeing fell 0.8% after the Federal Aviation Administration said Sunday that more than 300 Boeing 737 jets may have faulty parts. The FAA said it is forcing airlines to remove and replace any plane parts that are affected. The FAA said as many as 148 parts could be "susceptible to premature failure or cracks."

—CNBC's Maggie Fitzgerald and Nadine El-Bawab contributed to this report.