LONDON — Gene therapy has cured two dying men of cancer by using genetically modified versions of their own cells.

Both were suffering from advanced melanoma, but the technique could be customized to attack other common cancers.

Although scientists remain cautious because many false leaps forward have occurred in the use of gene therapy, the results show, in principle at least, that aggressive cancer can be treated this way, even after it has spread and the outlook is grim.

Mark Origer, 53, told the Daily Telegraph last night how, after five years of losing the battle with the disease, he was made well enough to attend his daughter’s wedding last year.

“She wanted me to be there for her, and she wanted me to be there for me,” he said.

Mr. Origer, the head of the U.S. post office in Lake Mills, Wis., was diagnosed with melanoma — the most aggressive form of skin cancer — in 1999.

A cyst which grew on the same area of his back in 2002 was found to have malignant cells, and the cancer continued to spread until, in June 2004, it was found in his liver. He underwent various chemical and surgical treatments, but none was found to stop the spread of cancer.

In December 2004, he was given the gene therapy and was discharged the same month.

By January 2005, his tumors had shrunk by half and, by last September, when he attended his daughter Katie’s wedding, one small spot remained in his liver which surgeons removed.

Last week, doctors pronounced him completely clear of cancer cells.

Of the 17 patients with advanced skin cancer who underwent gene therapy, the treatment worked only on Mr. Origer and “Thomas M.,” aged 39, clearing the disease from liver, lymph node, and lung.

But scientists believe they can improve the response and adapt it to fight other cancers, notably breast, colon, and lung.

The success using the patients’ genetically modified white blood cells was reported yesterday in the journal Science by a team at America’s National Cancer Institute in Bethesda, Md., led by a pioneer in the field, Dr. Steven Rosenberg.

He said: “Both patients are still free of the disease after 18 months.”

During the study, tumors shrank in other participants, all of whom had exhausted other forms of treatment.

“It is the first time, with all the hype of gene therapy, we have managed to use genetic engineering to treat cancer patients,” Dr. Rosenberg said.

The institute director, Dr. John Niederhuber, said: “These are very exciting successes. They bring hope that this type of gene therapy could be used in many types of common cancers and could be achievable in the near future.”

Alan Kingsman of Oxford Bio-Medica, a British company developing gene therapy and vaccines to fight cancer, said: “This is an excellent piece of work and shows the huge therapeutic potential of immune therapy.”

The treatment relies on the body’s protective immune system, in this case a type of white blood cell, or lymphocyte, called a T-cell. Although they attack tumors, these alone are no match for an aggressive cancer.

Dr. Rosenberg created billions of T-cells by removing the patients’ cells and modifying them so they developed a certain receptor, a protein that helps them to recognize and kill tumors.

Genetically engineered cells were transfused into 17 patients with advanced metastatic melanoma, where the disease had spread.

The study shows that the engineered cells can shrink large tumors.

Dr. Rosenberg has found a more potent class of receptors, up to 100 times more effective at helping immune cells attack the cancer. His team has also engineered immune cells to attack breast, lung, and liver cancers.

“We have now expressed other lymphocyte receptors that recognize breast, lung, and other cancers,” he said. “They are present on half of all common cancers. We can, with these powerful receptors, convert any patient’s normal cells into cells that will recognize these common cancers.”

Trials will start within a month, subject to approval by the American authorities, though Dr. Rosenberg did not want to identify which cancer types would be involved.