AbbVie announced it is buying cancer drug-maker Pharmacyclics for $21 billion. Through the deal, AbbVie will receive access to Pharmacyclics' flagship product, Imbruvica, which is FDA-approved to treat three different types of blood cancers. Feuerstein says Imbruvica is known to be very effective and is expected to generate about $1 billion in sales this year. However, AbbVie will only receive half of Imbruvica for the $21 billion it's spending, because the other half of the drug is owned by Johnson & Johnson. TheStreet senior columnist Adam Feuerstein explains why AbbVie is spending so much money to receive only half of a drug and how the deal stands to impact not just the company, but the overall biotech sector.