“We’re barely able to afford the treatment I’m already getting,” Ms. Kudesia, 48, said with quiet defiance. “My kids are just starting out in life. There is no way I’m going to be a burden to them.”

The drug, Herceptin, is one of the most effective treatments for an aggressive form of breast cancer. But in India, at a cost of at least $18,000 for one course of treatment, only a small fraction of the women who need it get it.

The Indian government last year threatened to allow production of less costly, generic versions of Herceptin. Its maker, Roche Holdings of Switzerland, initially resisted, but surrendered its patent rights this year in large measure because it concluded that it would lose a legal contest in Indian courts.

The skirmishing over Herceptin and other cancer medicines is part of a new and critical phase in a struggle to make drugs affordable to the world’s poorest people, one that began in earnest more than a decade ago when advocates campaigned successfully to make AIDS medicines accessible to millions of Africans.

“Cancer is the next H.I.V./AIDS issue, and the fight has only begun,” said Shamnad Basheer, a professor of law at West Bengal National University of Juridical Sciences in Kolkata.

American trade officials have voiced concerns about India’s treatment of drug patents, including its reasons for sometimes overriding them. President Obama discussed the issue this year with Prime Minister Manmohan Singh of India in the Oval Office, administration officials said.

Executives in the international pharmaceutical industry, increasingly dependent on drug sales in emerging markets like India, China and Brazil, contend that India’s efforts to cancel patents threaten the global system for discovering cures while doing little to resolve the health challenges most patients here face.

“We are open to discussing what the best way is to bring innovative medicines to patients,” said Daniel Grotzky, a spokesman for Roche, which has a large portfolio of cancer medicines. “But a society that wants to develop new medicines and technology must reward innovation through a solid protection of intellectual property.”

Some health experts say investing in earlier diagnosis of breast cancer and improved testing, surgery and access to radiation therapy is more important than access to expensive drugs. “Chemotherapy is not the major issue for cancer control in India,” said Dr. Richard Sullivan, a professor of cancer policy and global health at King’s Health Partners’ Integrated Cancer Center in London.

But health advocates say similar arguments were made by the United States government and the pharmaceutical industry as they sought to protect patents on AIDS medicines through much of the 1990s, a stance that former President Bill Clinton has since said he regrets. It would be unfair to delay improving access to cancer drugs until India’s broken system for cancer care was fixed, they say. They note that more than twice as many people in India die of cancer than of AIDS.

As the world has made progress against malnutrition and infectious diseases, more people are living into old age and dying of chronic illnesses like heart disease and cancer, which now cause two-thirds of deaths globally. In 2012, there were 14.1 million new cancer cases across the world and 8.2 million cancer deaths, according to the World Health Organization. And the number of breast cancer cases is growing. About 6.3 million women were living with the disease last year.

The rise in the cancer caseload is already a heavy burden on India’s hobbled health system. Indian women, while less likely to get breast cancer than those in the United States, are far more likely to die of it. Breast cancer is diagnosed in about 115,000 women here every year, and in 2008 some 54,000 died from it, according to the World Health Organization.

At intersections in New Delhi, women carrying doctors’ notes beg for money for their prescribed treatments. India has just 27 dedicated public cancer centers for 1.2 billion people. The government has promised to add an additional 50 in the coming years, but medical experts say even that will be grossly inadequate.

India, which is one of the world’s leading producers of generic pharmaceuticals, has long viewed patent rights on medicines skeptically. It has already ruled invalid patents protecting exclusive sales of Novartis’s Gleevec, Pfizer’s Sutent and Roche’s Tarceva, all cancer medicines. In a landmark decision last year, the government agreed that the patent protecting Bayer’s Nexavar, also a cancer drug, was valid but overrode it anyway because a generic company promised to lower the price from $4,500 to about $140 per month of treatment.

The government is now considering canceling the exclusive sales rights on two other cancer medicines. Roche Holdings surrendered its patent on Herceptin this year in part because it viewed it as a losing battle. Each of these steps was greeted with acclaim in India and deep disapproval from business groups, legislators and drug makers in the United States.

An Indian government committee is soon expected to announce the start of a formal process to set aside patents on 15 more medicines, according to a committee member who agreed to speak about secret deliberations only if granted anonymity. Malini Aisola of the Public Health Foundation of India said the expanded list “will create ripples around the world.”

For drug companies, the most worrisome aspect of India’s efforts to lower drug prices is that other countries are beginning to follow its lead. Both Indonesia and the Philippines recently adopted patent laws modeled on India’s, and legislators in Brazil and Colombia have proposed following suit.

“One of the concerns of the industry is not just what India is doing in India, but we realize that the whole world is watching India,” said Amy Hariani of the U.S.-India Business Council, which is affiliated with the U.S. Chamber of Commerce and is fighting India’s patent policies.

Even insured patients in the United States may wonder why they are making thousands of dollars in co-payments if these medicines cost far less in India. Treatment with Herceptin is even more expensive in the United States, so even Medicare patients must make thousands of dollars in co-pays.

“Why should we be giving away Herceptin in India and China when we have insured women in the United States who can’t even afford the co-pay?” asked Dr. Peter Bach, a drug price expert at Memorial Sloan-Kettering Cancer Center. “Nobody really asked that question about AIDS drugs in Africa. But with cancer medicines, people will ask, and that’s what scares the pharmaceutical industry.”

For the Obama administration, the fight over drug patents in the developing world is a minefield. The drug industry was a major contributor to Mr. Obama’s campaign and an early and crucial backer of his health care program. But Mr. Obama’s advisers hope to avoid the mistakes of the Clinton administration, which was harshly criticized by AIDS activists for its initial stand against providing generic antiretroviral drugs to Africa.

Vice President Joseph R. Biden Jr., during a July visit to India, discussed the importance of balancing patent rights and access to medicines with the prime minister, while Mr. Obama and Mr. Singh spoke about the issue in September, administration officials said.

A report released in May by the Office of the United States Trade Representative listed multiple concerns with India’s treatment of drug patents, including its high bar for obtaining patents. Trade officials also pointed to a 2012 blog post by Teresa Stanek Rea, then the deputy director of the United States Patent and Trademark Office, that stated that “we encourage our trading partners to consider ways to address their public health challenges while maintaining intellectual property rights systems that promote investment, research, and innovation,” and that India “may undermine those goals.”

Roche’s decision to surrender its Herceptin patent has had a rapid impact on the market here in India. Last month, Biocon, an Indian drug maker, announced that it had won approval for a generic, less expensive version of the drug, which the company expects to begin selling early next year.

Manjeet Kaur, 51, of New Delhi, may benefit. Her husband, an account manager at a technology service company, spent his life savings on a full course of Herceptin for her. Every three weeks, the couple takes two vials of the medicine to the All India Institute of Medical Sciences, a vast and chaotic warren of buildings widely considered the nation’s premier hospital.

She often waits many hours for the life-sustaining infusion. On a recent day, she sat cross-legged, wrapped in a saffron scarf, in a room with six other women. Outside, hundreds of people lined up hoping for care.

About 25,000 Indian women would benefit from Herceptin treatment every year, but at most only 1,500 get it, according to Kalyani Menon-Sen, a patient advocate in New Delhi who led a campaign for a generic version.

Ms. Kudesia, afraid to tell her children about Herceptin because of its cost, is already having trouble affording her cocktail of less expensive generic medicines.

She said she discovered something was wrong with her after a stray cow bruised her right breast with its horn while she was bowing to touch its hoof in a sign of respect for an animal sacred to Hindus. A doctor prescribed painkillers, but her discomfort only grew. Another doctor took an X-ray and said her shoulder was swollen. Then she got a mammogram, which showed cancer.

Her daughter borrowed $1,600 from a bank for her mastectomy. After begging relatives, Ms. Kudesia got the nearly $2,000 she needed for three rounds of chemotherapy. She needs more treatment, but has no idea where the money will come from. Her husband died in 2011 from a brain tumor, and his three-year treatment drained their savings.

To save money, she said, she must now move out of the three-room, $80-per-month apartment she shares with her mother-in-law and son and sell most of their possessions. Buying Herceptin is out of the question. She prays to Krishna, Rama and other Hindu gods for help.

“I want to spend the rest of the time I have left resolving our debts, not making them worse,” she said. “I cannot tell my children there is another drug that will help me.”