Shares of Alexion Pharmaceuticals (ALXN) dipped in after-hours trading Wednesday after the company confirmed a delay in its quarterly regulatory filing, appearing to confirm research firm Leerink's warnings on the matter late last week.

BACKGROUND: On November 4, rumors began circulating that Alexion had cancelled a conference appearance, spurring a spike in the stock as investors speculated whether a takeover could be in the works. While Bloomberg later confirmed the conference cancellation and Gilead (GILD) was named as one hypothetical acquirer, research firm Leerink highlighted that the company's seemingly delayed quarterly regulatory filing could be the more worrisome event.

ALEXION CONFIRMS 10-Q DELAY AMID SALES PROBE: After being halted for trading shortly after 4 pm ET on November 9, Alexion announced it has filed a formal 10-Q delay due to an investigation into recent allegations by a former employee "with respect to the company's sales practices of Soliris, or eculizumab." The probe centers around whether employees "have engaged in sales practices that were inconsistent with company policies and procedures," though the company cautioned that "at this point in time," it hasn't identified instances where Soliris orders were not placed by customers for patients or any facts that require the company to update previously reported results.

LEERINK HITS MARK WITH EARLY WARNING: In a November 4 research note responding to the Alexion rumors, Leerink's Geoffrey Porges and Bradley Canino highlighted that the company's delayed 10-Q filing "seems more significant than the withdrawal from the conference to us, and should not be interpreted as only positive." The analysts explained that, while not technically past its filing deadline, Alexion typically submits its 10-Q within one day of posting quarterly results, which were reported on October 27. After reaching out to the company, Porges said Alexion "acknowledged" the apparent delay and, when asked about the event cancellation, said only that "something came up." Arguing that the conference news was not necessarily material given the lack of senior executives or public Q&A sessions, Porges pinned the 10-Q delay as the more worrisome issue and warned investors that something appeared "afoot" at the drugmaker.

PRICE ACTION: Shares of Alexion fell 2.45% to $124.05 in post-market trading Wednesday.