(Reuters) - Amgen Inc on Wednesday said its new type of treatment for a deadly form of leukemia would cost about $178,000 when it becomes available on Thursday, which would make it one of the world's most expensive cancer drugs.

Company spokeswoman Danielle Bertrand said the price for the infused medicine, called Blincyto, would reflect two courses of treatment, at $89,000 per cycle.

"We believe the price reflects the significant clinical, economic and humanistic value of the product to patients and the healthcare system, for an ultra-orphan population with a dramatic impact on a serious illness," Amgen said in an emailed statement.

The world's largest biotech company also said the price reflects the complexity of developing and making innovative biotech drugs.

U.S. regulators on Dec. 3 approved the Amgen drug more than five months ahead of the expected decision date, to treat a blood cancer called acute lyphoblastic leukemia (ALL), for which there are few options once a patient has relapsed following standard treatment.

The initial approval is for patients whose cancer has returned after treatment or did not respond to previous treatment, such as a stem cell transplant or chemotherapy.

In a clinical trial used for the approval decision, 32 percent of patients achieved complete remission for nearly seven months after receiving the drug via infusion for four weeks.

An estimated 6,020 Americans in 2014, almost half of them children, will be diagnosed with ALL and 1,440 will die from the disease, according to the National Cancer Institute. It is the most common form of leukemia affecting children.

Amgen acquired Blincyto through its $1.2 billion purchase in 2012 of Micromet, a biotechnology company founded in Germany. At the time, Blincyto was known by its chemical name, blinatumomab.

The drug is a so-called bispecific antibody, a hot emerging technology that could prove more potent than conventional antibodies, which have become mainstay treatments for a wide array of cancers. Antibodies are proteins that look out for "foreign" invaders such as bacteria, as well as for aberrant fast-growing cells like cancer.

The Y-shaped proteins have two arms that bind the same protein target found on cancer cells, in an attempt to neutralize the cells. With bispecific antibodies, however, one arm grasps the cancer cell, while the other takes hold of an immune system defender called a T cell, bringing the enemies into contact and leading to destruction of the cancer cell.

Immuno-oncology drugs, which stimulate the immune system or prevent tumor cells from hiding themselves, have become a main focus of drugmakers, following approval in 2011 of Bristol-Myers Squibb Co's Yervoy treatment for melanoma. It costs about $120,000 for a complete course of four infusions.

Yervoy and members of another class of drugs called PD-1 inhibitors, including Merck & Co's recently approved Keytruda, work by removing a brake on the immune system. Keytruda costs about $150,000 for a year of treatment.

(Reporting by Ransdell Pierson; Editing by Lisa Von Ahn and David Gregorio)