Elena, a cancer patient, at a clinic in Athens. Her illness long went untreated.

ATHENS — As the head of Greece’s largest oncology department, Dr. Kostas Syrigos thought he had seen everything. But nothing prepared him for Elena, an unemployed woman whose breast cancer had been diagnosed a year before she came to him.

By that time, her cancer had grown to the size of an orange and broken through the skin, leaving a wound that she was draining with paper napkins. “When we saw her we were speechless,” said Dr. Syrigos, the chief of oncology at Sotiria General Hospital in central Athens. “Everyone was crying. Things like that are described in textbooks, but you never see them because until now, anybody who got sick in this country could always get help.”

Life in Greece has been turned on its head since the debt crisis took hold. But in few areas has the change been more striking than in health care. Until recently, Greece had a typical European health system, with employers and individuals contributing to a fund that with government assistance financed universal care. People who lost their jobs received health care and unemployment benefits for a year, but were still treated by hospitals if they could not afford to pay even after the benefits expired.

Things changed in July 2011, when Greece signed a supplemental loan agreement with international lenders to ward off financial collapse. Now, as stipulated in the deal,  Greeks must pay all costs out of pocket after their benefits expire.

About half of Greece’s 1.2 million long-term unemployed lack health insurance, a number that is expected to rise sharply in a country with an unemployment rate of 25 percent and a moribund economy, said Savas Robolis, director of the Labor Institute of the General Confederation of Greek Workers. A new $17.5 billion austerity package of budget cuts and tax increases, agreed upon Wednesday with Greece’s international lenders, will make matters only worse, most economists say.

The changes are forcing increasing numbers of people to seek help outside the traditional health care system. Elena, for example, was referred to Dr. Syrigos by doctors in an underground movement that has sprung up here to care for the uninsured. “In Greece right now, to be unemployed means death,” said Dr. Syrigos, an imposing man with a stern demeanor that grew soft when discussing the plight of cancer patients.

The development is new for Greeks — and perhaps for Europe, too. “We are moving to the same situation that the United States has been in, where when you lose your job and you are uninsured, you aren’t covered,” Dr. Syrigos said.

The change is particularly striking in cancer care, with its lengthy and expensive treatments. When cancer is diagnosed among the uninsured, “the system simply ignores them,” Dr. Syrigos said. He said, “They can’t access chemotherapy, surgery or even simple drugs.”

The health care system itself is increasingly dysfunctional, and may worsen if the government slashes an additional $2 billion in health spending, which it has proposed as part of a new austerity plan aimed to lock down more financing. With the state coffers drained, supplies have gotten so low that some patients have been forced to bring their own supplies, like stents and syringes, for treatments.

Hospitals and pharmacies now demand cash payment for drugs, which for cancer patients can amount to tens of thousands of dollars, money most of them do not have. With the system deteriorating, Dr. Syrigos and several colleagues have decided to take matters into their own hands.

Earlier this year, they set up a surreptitious network to help uninsured cancer patients and other ill people, which operates off the official grid using only spare medicines donated by pharmacies, some pharmaceutical companies and even the families of cancer patients who died. In Greece, doctors found to be helping an uninsured person using hospital medicines must cover the cost from their own pockets.

At the Metropolitan Social Clinic, a makeshift medical center near an abandoned American Air Force base outside Athens, Dr. Giorgos Vichas pointed one recent afternoon to plastic bags crammed with donated medicines lining the dingy floors outside his office.

“We’re a Robin Hood network,” said Dr. Vichas, a cardiologist who founded the underground movement in January. “But this operation has an expiration date,” he said. “People at some point will no longer be able to donate because of the crisis. That’s why we’re pressuring the state to take responsibility again.”

In a supply room, a blue filing cabinet was filled with cancer drugs. But they were not enough to take care of the rising number of cancer patients knocking on his door. Many of the medicines are forwarded to Dr. Syrigos, who set up an off-hours infirmary in the hospital three months ago to treat uninsured cancer patients Dr. Vichas and other doctors in the network send his way.

Dr. Syrigos’s staff members consistently volunteer to work after their official shifts; the number of patients has risen to 35 from 5. “Sometimes I come home tired, exhausted, seeing double,” said Korina Liberopoulou, a pathologist on site one afternoon with five doctors and nurses. “But as long as there are materials to work with, this practice will go on.”

Back at the medical center, Dr. Vichas said he had never imagined being so overwhelmed with people in need.

As he spoke, Elena appeared, wearing a pleated gray head wrap and a loose plum blouse. She was coming for drugs to help her cope with the aftermath of chemotherapy she had recently received from Dr. Syrigos.

Elena said she was left without insurance after quitting her teaching job to care for her cancer-stricken parents and a sick uncle. By the time they died, the financial crisis had hit Greece and, at 58, it was impossible for her to find work.

She said she panicked when she was found to have the same type of breast cancer that killed her mother: the treatments would cost at least $40,000, she was told, and her family’s funds were depleted. She tried to sell a small plot of land, but no one was buying.

Her cancer spread, and she could not find treatment until a few months ago, when she sought out Dr. Vichas’s underground clinic after hearing about it through word of mouth. “If I couldn’t come here, I would do nothing,” she said. “In Greece today, you have to make a contract with yourself that you will not get very sick.”

She said she was dismayed that the Greek state, as part of the bailout, had pulled back on a pillar of protection for society. But the fact that doctors and ordinary Greeks were organizing to pitch in where the state failed gave her hope in her bleakest hours. “Here, there is somebody who cares,” Elena said.

For Dr. Vichas, the most powerful therapy may not be the medicines, but the optimism that his Robin Hood group brings to those who have almost given up. “What we’ve gained from the crisis is to come closer together,” he said.

“This is resistance,” he added, sweeping his eyes over the volunteers and patients bustling around the clinic. “It is a nation, a people allowed to stand on their own two feet again with the help they give each other.”

Dimitris Bounias contributed reporting.