Rigel, Merck Form Development Partnership  NEW YORK (Reuters) - Biotechnology company Rigel  Pharmaceuticals Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=RIGL.O target=/stocks/quickinfo/fullquote"&gt;RIGL.O&lt;/A&gt; has entered into a collaboration  pact with drugmaker Merck   Co. Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MRK.N target=/stocks/quickinfo/fullquote"&gt;MRK.N&lt;/A&gt; to find treatments  for cancer and potentially other diseases, Rigel said on  Monday.