5. SIGNIFICANT CONCENTRATIONS

We recognize revenue on collaborations in the U.S. and abroad and on products sold solely in the U.S. For the year ended December 31, 2018, Kissei and our three specialty distributors (see Note 2) accounted for 69% and 31% of our total revenues, respectively. For the year ended December 31, 2017, BerGenBio and another unrelated third party accounted for 74% and 26% of our total revenues, respectively. For the year ended December 31, 2016, BMS and BerGenBio accounted for 82% and 18% of our revenues, respectively. As of December 31, 2018, 100% of our accounts receivables are from three customers. We had no accounts receivable as of December 31, 2017.