What happened

Shares of Illumina (ILMN 0.48%) were tumbling 10.1% lower this week as of the market close on Thursday, according to data from S&P Global Intelligence. Most of the decline came after a European Union court ruled on Wednesday that an antitrust investigation into Illumina's acquisition of Grail can move forward. EU regulators opposed Illumina's $8 billion buyout of Grail due to concerns that it would give Illumina too much control of the genetic-sequencing testing market.

So what

It's not surprising that the genomics stock is falling this week. Should the acquisition of Grail ultimately be thwarted, it could seriously hurt Illumina's opportunity to expand beyond its core genomic-sequencing business.

Illumina technically completed its acquisition of Grail in August 2021. However, the company has operated Grail as a separate unit while the EU investigation proceeded. Illumina challenged the antitrust probe in the EU court.  

Grail was originally formed by Illumina, but the company spun the unit off in early 2016. Illumina decided to reunite with Grail because of its tremendous growth prospects in detecting early-stage cancer. The company thinks that this market could reach $46 billion by 2035. Cancer monitoring could represent an additional $14 billion market.

Now what

The story is far from over. Illumina told Reuters that it plans to appeal the EU court's ruling. The company also continues to work with the European Commission to try to identify remedies that could pave the way for the acquisition of Grail to win approval.