July 15 (Reuters) - Shares of Celcuity ( CELC ) fell about 8% in premarket trading on Wednesday, as the delayed commercial launch of its newly approved breast cancer drug and treatment-tolerability concerns overshadowed the company's first U.S. approval.

The U.S. Food and Drug Administration on Tuesday approved gedatolisib, branded as Revtorpyk, for certain patients with advanced breast cancer whose tumors do not carry a PIK3CA mutation.

The approval gives Celcuity ( CELC ) its first marketed product, which is expected to launch late in the third quarter, as management cites the need to ensure adequate drug supply.

The company did not disclose a launch price, but noted that Revtorpyk would be at a premium to currently available therapies, Needham analyst Gil Blum said.

The approval was largely expected, but the launch delay was not, given Celcuity's ( CELC ) earlier comments about launch readiness, Leerink Partners analyst Andrew Berens said.

Revtorpyk, combined with Pfizer's ( PFE ) Ibrance and fulvestrant, reduced the risk of disease progression or death by 76% in a late-stage trial.

Patients receiving the treatment went a median 9.3 months without their cancer worsening, compared with two months for those receiving fulvestrant alone.

Revtorpyk's label showed that 12% of patients receiving the three-drug combination stopped treatment due to side effects.

The label warns that Revtorpyk can cause severe mouth inflammation and recommends preventive mouthwash. Mouth inflammation occurred in 72% of patients receiving the three-drug combination, including severe cases in 22%.

Celcuity's ( CELC ) ability to help doctors manage mouth inflammation and keep patients on the drug would be critical to its commercial success, Berens said.