Preliminary trials on humans are underway for a new form of cancer treatment developed by Cambridge-based Repligen Corporation, company officials said yesterday.

Repligen has been working on the drug since 1987, said Ramesh Ratan, senior vice president of the firm. The first human clinical trials, or phase one, began on AIDS patients afflicted with Kaposi's sarcoma--a type of skin cancer--in late June of 1992.

According to Ratan, results from these safety trials on the drug, Replistatin, are expected in late December.

So far no adverse reactions to the drug have been observed, company reports say.

All of the phase one tests will be complete by the end of next month, but the exact results will not be known for another month or so.

Replistatin's potential as a cancer treatment rests in its ability to prevent the formation of blood vessel networks vital to the growth of tumors and lesions, according to a Repligen report.

In addition, Replistatin may be used to neutralize the effect of heparin, a drug used in cardiovascular procedures to prevent blood clotting.

Heparin neutralization is required in nearly all of the cardiopulmonary bypass procedures performed each year in the U.S.

After the conclusion of the first phase of clinical trials, Repligen plans to conduct two other phases of testing for efficacy of the drug. Ratan said he hopes to receive approval of the Food and Drug Administration for Replistatin by the year 1998.

While it is a long-term investment--Repligen does not expect to be able to market the drug until it is approved by the FDA--Ratan projects a potential market of $200 million.