The basic reason behind why Gilead Sciences trades at a very modest FY15 P/E of 10.8 is that the company is highly dependent on its unique blockbuster HCV drugs Sovaldi and Harvoni.

Although the company has diversified product portfolio and a promising pipeline, the HCV products based on the antiviral agents sofosbuvir and ledipasvir will carry on to dominate in the future.

Presently, Gilead has the superior regimen, which is applicable to more HCV genotypes. They have least side effects and also are the most convenient.

But the question is how many people will receive treatment, and how the market price will develop. All this will ultimately determine how high the peak sales for Sovaldi and Harvoni will be and when will this rise will be observed.

Furthermore, a discount for Gilead's HCV business is justified and its valuation cannot be aligned with the other major biotech companies.

It has been said that antiviral products without Sovaldi/Harvoni and 'Other Products' generated revenues of $12,064M in 2014. And in 2013, Gilead reported revenues of $10,804M and a net income $3,075M, which corresponds to a net income margin of 28.7%.

This in total leads to a calculated net income of $3,458M for Gilead's non-HCV drugs in 2014. And if the company's business can grow at the same rate, 2015 revenues will grow to $13.6B and net income to $3.9B.

It seems that Sovaldi and Harvoni will continue to be the main cash generators for Gilead, and a significant amount of this cash will be spent for buybacks, which in turn will grow EPS.