For the last 4 decades, scientists have been calling for styrene, a chemical found in Styrofoam cups and packaging, to be studied further to determine if it causes cancer. Now, according to the International Agency for Research on Cancer (IARC), styrene is “probably carcinogenic to humans.” 
Styrene was previously classified as “possibly carcinogenic to humans.”
Research shows that workplace styrene exposure doubles the risk of leukemia, and increases the risk of a certain type of nasal cancer by 5 times. 
Most people come into contact with the chemical through cigarette smoke, air pollution, printers, or photocopiers. The authors of the announcement, which will be published as a Monograph, said exposure to styrene at work is a global problem.  
A team of 23 scientists hand-picked by the IARC looked at the records of more than 70,000 people who worked in the Danish plastics industry between 1968 and 2011. The team also reviewed evidence from animal studies on the health risks of styrene exposure.  
Professor Henrik Kolstad of Aarhus University in Denmark said:
“The most recent styrene study shows the risk of acute myeloid leukemia, a rare form of leukemia, is doubled.
Out of the more than 70,000 people included in the research project, we found 25 cases of acute myeloid leukemia, where you would statistically expect to find 10.”
The American Cancer Society (ACS) estimates that 19,520 new cases of acute myeloid leukemia will be diagnosed in the U.S. in 2018, and the disease is expected to kill 10,670 people. 
The study also found a 5-fold increase in the risk of sinonasal adenocarcinoma, a nasal cancer, among study subjects who were exposed to the chemical while working in the plastics industry. 
In addition to Styrofoam, styrene is used in synthetic rubber, some insulation materials, disposable cutlery, plastic packaging, and fiberglass plastic.
The U.S. Centers for Disease Control (CDC) has warned that people may be exposed to small amounts of styrene if it gets into food packaged in polystyrene containers, including Styrofoam.
The researchers also looked for potential links between styrene exposure and Hodgkin lymphoma, and T-cell lymphoma, but did not spot the same link.
 Science Daily
 Daily Mail