* Earnings beat estimates in 3rd qtr

* Humira sales also top analyst projections

* AbbVie sees future growth from cancer drugs

* Boosts dividend 11 percent

* Shares up 4 percent (Adds analyst comment, updates share price)

By Tamara Mathias and Anuron Kumar Mitra

Oct 27 (Reuters) - AbbVie Inc forecast its flagship drug Humira to bring $21 billion in sales by 2020, about $3 billion higher than its expectation two years ago, driving the U.S. drugmaker's shares up 4 percent on Friday.

AbbVie also reported third-quarter earnings above Wall Street estimates, as it sold more of Humira — the world's best selling prescription medicine — and Imbruvica, its other main drug. The company also raised its annual earnings forecast.

Humira, which is approved to treat psoriasis and rheumatoid arthritis, generated sales of $4.70 billion in the third quarter ended Sept. 30, topping analysts' average estimate of $4.66 billion, according to analysts at Jefferies. The drug raked in just over $16 billion last year.

"In a very choppy earnings season, have to hand it to AbbVie for delivering," Evercore ISI analyst Joshua Schimmer said.

Last month, AbbVie reassured investors that Humira would be safe from competition for at least a few more years, granting rival Amgen Inc a non-exclusive license to sell a copycat version in the United States, but not before 2023.

However, on a call with analysts, AbbVie talked up the potential of its other drugs.

The drugmaker said cancer treatments such as Imbruvica and Rova-T - which is in development - will drive future growth and help lower its reliance on Humira, which makes up two-thirds of overall sales.

AbbVie expects non-Humira sales to exceed $35 billion by 2025 from about $9.6 billion this year. It also expects to launch more than 20 products by 2020.

AbbVie's growth should be sustainable for the next few years as its drug pipeline develops, Evercore ISI's Schimmer said.

The Chicago-based company is also targeting Alzheimer's disease, the women's health space and Hepatitis C.

Two of its other drugs - upadacitinib and risankizumab - have been successful in recent trials, possibly opening up billion-dollar markets if approved by regulators.

AbbVie's shares, up 43 percent so far this year, were up 3.7 percent at $92.91 in late morning trading on Friday.

The company's net earnings rose 2.1 percent to $1.63 billion in the third quarter. Excluding one-time items, it earned $1.41 per share, topping analysts' expectations of $1.38, according to Thomson Reuters I/B/E/S.

Net revenue climbed 8.8 percent to $7 billion, matching analysts' estimates.

AbbVie also boosted its quarterly dividend payout 11 percent to 71 cents per share.

It lifted its forecast for 2017 adjusted earnings to $5.53 to $5.55 per share from $5.44 to $5.54. (Reporting by Tamara Mathias and Anuron Kumar Mitra in Bengaluru; Editing by Sai Sachin Ravikumar)