NEW YORK (CNNMoney.com) -- Genentech reported third-quarter net earnings Tuesday that topped expectations, but shares for the biotech developer fell in after-hours trading because of concern about some drug sales.

Genentech (down $0.68 to $85.60, Charts) posted earnings of 53 cents a share, a 36 percent year-to-year jump that beat estimates. It also reported operating revenues of $2.38 billion, a 36 percent jump that also beat expectations.

Analysts consensus was expecting third quarter sales of $2.32 billion and earnings per share of 51 cents, according to Thomson First Call.

But sales for two cancer drugs - Rituxan and Herceptin - were down from the second quarter, and sales for a third cancer treatment, Avastin, were only slightly better. The drugs made significant jumps in year-to-year comparisons for the quarter.

Third-quarter sales for Rituxan, a treatment for non-Hodgkin's lymphoma and rheumatoid arthritis, and the biotech's top earner, increased 12 percent from a year earlierr to $509 million, but fell from $526 million in the prior three months.

Sales for Herceptin, a breast cancer drug, experienced a 40 percent sales surge year over year, to $302 million, but were down from $320 million in the preceding quarter.

Sales of Avastin, a colon cancer drug, jumped 34 percent from the prior year, to $435 million. It was up just slightly from $423 million in the quarter ended in June.

Sales for Lucentis, a treatment for age-related vision loss, reached $153 million, and was largely responsible for driving company sales. The drug is relatively new, having been approved by the Food and Drug Administration and launched June 30.

Ian Clark, executive vice president of commercial operations for Genentech, said in a Webcast with analysts that Lucentis was taking market share from Pfizer's (down $0.09 to $27.56, Charts) Macugen and Novartis' (down $0.27 to $57.74, Charts) Visudyne, but the market for age-related vision loss treatment is not increasing in size.

This means that Lucentis will eventually have to retain new patients to keep growing, said Clark.

Rahul Jasuja, analyst for MDB Capital Group, said sales have been "really stellar" for Lucentis, which has "cannibalized" 80 percent of its sales from Macugen and Visudyne. Jasuja believes that Lucentis still has room to grow before the market taps out, and projects that annual U.S. sales will peak at $1.5 billion in three years.

Genentech, based in South San Francisco, Calif.,is the second-biggest biotech in the world in terms of sales. Amgen (down $0.19 to $73.73, Charts), based in Thousand Oaks, Calif., is the world's leader for Big Biotech, and plans to announced third quarter earnings Oct. 23.

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