(Adds company and analyst comments, updates share price)
July 27 (Reuters) - Bristol-Myers Squibb Co shares fell 4 percent on Thursday as investors bet that a failed cancer-drug trial at AstraZeneca Plc would have negative implications for Bristol-Myers' similar immunotherapy treatment regimen.
AstraZeneca's Mystic study, released Thursday, looked at a combination of immune system-boosting drugs to treat non-small cell lung cancer (NSCLC). The trial found it was no more effective than chemotherapy in improving the amount of time patients lived without their disease getting worse.
Bristol-Myers is studying a similar combination of its two top drugs in the same therapy class, Opdivo and Yervoy. Its shares were down 4 percent at $53.71 in midday trading.
So far, Merck & Co Inc's Keytruda is the only immunotherapy that has been approved as an initial treatment for NSCLC, the most common form of the disease.
Merck shares were up 4 percent on Thursday.
Asked about the implications of AstraZeneca's results during a conference call with analysts and investors, Bristol-Myers Chief Executive Officer Giovanni Caforio said: "It is difficult to speculate on a comparison."
He said the trials involved different drugs, dosing schedules, enrollment sizes and other factors.
Caforio said Bristol-Myers expects to see some results of its trial in the first quarter of 2018, noting an "opportunity for interim results in overall survival by the end of this year."
Also on Thursday, Bristol-Myers reported second-quarter results that largely met analyst expectations.
Sales of Opdivo surged 42 percent from a year earlier to $1.2 billion, while sales of Yervoy rose 34 percent to $322 million. Analysts, on average, expected Opdivo sales of $1.1 billion and Yervoy sales of $307 million, according to Thomson Reuters I/B/E/S.
"The Mystic results increase uncertainty about Bristol's immuno-oncology franchise, particularly Opdivo plus Yervoy in the important first-line NSCLC market, and therefore, in our view, lower the probability of Bristol being acquired as some on (Wall Street) expect," BMO Capital Markets analyst Alex Arfaei said in a research note.
Quarterly sales of blood thinner Eliquis, another important Bristol-Myers drug, jumped 51 percent from a year earlier.
Excluding items, Bristol-Myers earned 74 cents a share, matching the average analyst estimate. Revenue for the quarter rose 6 percent to $5.1 billion.
The company raised the lower end of its forecast range for 2017 adjusted earnings to $2.90 from $2.85 a share, and left the top end unchanged at $3.
Net income for the quarter fell 21 percent to $916 million, while research and development costs rose 31 percent to $1.66 billion. (Reporting by Deena Beasley in Los Angeles; Additional reporting by Caroline Humer; Editing by Jeffrey Benkoe and Bernadette Baum)