SUNNYVALE, Calif. ( TheStreet) -- Pharmacyclics' ( PCYC) BTK inhibitor ibrutinib is an exceptionally effective drug for many B-cell cancers and will likely be approved and launched commercially well before most investors expect -- perhaps as early as the end of 2013. An initial U.S. approval application for ibrutinib in relapsed/refractory mantle cell lymphoma (MCL) will be filed by the end of the third quarter, Pharmacyclics says. If FDA sticks to its typical eight-month review period, ibrutinib could be approved in the middle of 2014. Ibrutinib, however, is not your typical cancer drug. FDA has already granted it three breakthrough therapy designations: relapsed/refractory MCL, Waldenstrom's Macroglobulinemia, and CLL/SLL for patients with deletion 17p. Ibrutinib will be the first breakthrough therapy to be reviewed by the FDA, so investors are watching closely to see what benefits (if any) Pharmacyclics receives for these designations. Let's take a closer look at what the ibrutinib FDA review timeline might look like, and why I believe a December approval is possible: We don't know the exact date Pharmacyclics and its partner Johnson & Johnson ( JNJ) will submit ibrutinib to FDA. I'm going to assume September 1, since it fits the "before the end of the third quarter" guidance given by the two companies. If FDA went about the ibrutinib review in the usual manner, the approval would be announced on May 1, 2014. I'd be shocked if FDA took this much time. More recently, FDA has been reviewing cancer drugs with alacrity. Ariad Pharmaceuticals' leukemia drug Iclusig was approved on Dec. 14, 2012 -- more than three months earlier than expected. Onyx Pharmaceuticals' multiple myeloma drug Kyprolis was approved one week early on July 20, 2012. If ibrutinib gets an Iclusig-like review, the approval would come in February 2014. A five-month review period would be nice, faster than normal, but would it be a prize big enough to justify the hoopla around FDA's breakthrough therapy designation? FDA created this new designation to "expedite the development and review of drugs for serious or life-threatening conditions." A five-month review hardly seems expeditious enough.