Janssen Biotech said it submitted an NDA today for ibrutinib, the cancer agent it’s been co-developing with Pharmacyclics. The Johnson & Johnson unit requested indications for previously treated patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL), and for use in mantle cell lymphoma (MCL).

If approved, the oral drug would be the first in the class known as BTK inhibitors. The filing is also getting careful attention from analysts who are eager to see how FDA assesses drugs it has awarded “breakthrough therapy designation,” specifically whether the agency lives up to its pledge to prioritize them.

Ibrutinib has actually received three breakthrough nods: for patients with CLL/SLL with “del 17p” (deletion of the short arm of chromosome 17), patients with relapsed/refractory MCL, and Waldenstrom’s macroglobulinemia (WM). It is not uncommon for patients to receive multiple lines of treatment over the course of their disease for CLL and SLL.

RCB Analyst Michael Yee pegged “eventual sales” for ibrutinib around $5 billion, according to Bloomberg. Ibrutinib’s draw, in part, lies in its oral formation and that it could eventually be used without chemotherapy, which is risky in CLL’s mostly elderly patient population. A Forbes report described it as “The Gleevec of CLL,” referring to the Novartis blockbuster initially approved for a rare form of leukemia and which now has 11 indications.

News also came yesterday that Pharmacyclics, which is co-developing the drug with Janssen, has asked the FDA for priority review of ibrutinib in hopes of shortening the FDA review period.

This is not without precedent. Roche received the breakthrough stamp for its own CLL candidate, GA101, in May, then scored priority review status from the agency earlier this month.

Yee, as reported by MarketWatch, was surprised by this move, but said in an analyst note: “We predict the drug is on the market before the end of this calendar year giving it at a least a year or even more ahead of Gilead and two years ahead of Abbvie and feedback from docs is Pharmacyclics [drug] will be used as first choice due to highest efficacy and cleanest safety.”

At the American Society of Clinical Oncology conference last month, both Gilead and AbbVie presented clinical data on their drug candidates for relapsed or refractory CLL. Gilead’s candidate, idelalisib, was tested in combination with rituximab in treatment-naïve patients with CLL. That regimen achieved a compete response rate of 19% and an overall response rate of 97% in patients.

AbbVie’s contender, ABT-199, which Yee cites as two years out, reported Phase I data at ASCO: In a study of 55 patients, 86% (44) achieved a response to ABT-199, while 10 patients achieved a complete response and 36 patients achieved a partial response.

The Cancer Institute estimates that 113,000 patients have CLL in the US and an additional 15,680 are diagnosed each year. CLL has a five-year survival rate of approximately 82%.