For those with a sufficiently long investment horizon, the stock looks attractive.Major market indexes such as the S&P 500 declined in the first few months of the year, but have since rebounded significantly. In contrast, biotech giant Amgen (AMGN 0.17%) started the year strong, but has not maintained that momentum. Over the past six months, Amgen's shares have declined by 9%. The drugmaker is facing some issues, including upcoming patent cliffs.Even so, there remain strong reasons to invest in Amgen and ho ...