Pros
Great opportunity to learn about cancer research from the very best. Medium-big company that behaves like a smaller one, with lots of freedom to design and perform experiments, propose improvements and learn along the way. Colleagues are great and there are plenty of opportunities for socialising with colleagues, such as sports clubs, drinks on Fridays, and toast when breakthroughs are achieved. If you want to be a successful researcher in cancer, Genmab is a great place.
Cons
As an intern you won't be invited to such toast for achievements, company's anniversary, etc. They also tend to pay in the lower side considering the highly educated professionals they employ. As a Research Associate, you will never be a Scientist without a PhD, so if you want to grow within R&D, you might consider doing one. Finally, people with a Master's degree join at the same position as others with applied science education or a Bachelor's degree.