But inside, cytologists peer through microscopes at 200,000 glass slides each year for signs of cervical cancer — finding abnormal cells in perhaps one in every 20.

"And there are three or four labs in the city even larger than us," said medical director Dr. Robert Bredt. "There are some labs here that do three-quarters of a million."

Gov. Rick Perry's recent decision to require 11- and 12-year-old girls to be vaccinated against the human papillomavirus before they can enter the sixth grade has generated considerable debate among parents, advocacy groups and lawmakers.

Perhaps lost in the uproar is the fact that medicine stands on the brink of starkly reducing women's odds of getting one of the world's deadliest cancers. Clinical trials of a second HPV vaccine also are under way in San Antonio and across the country.

"We do about 2 million evaluations per year for abnormal Pap smears in this country, which is hugely expensive, and most of those are for HPV-type changes," said Dr. Kevin Hall, chief of gynecology/oncology at the University of Texas Health Science Center.

In Bexar County in 2005, the most recent year local numbers are available, 19 women died — down from 30 the previous year. The rate of disease among Hispanic women nationwide is more than twice that of non-Hispanic whites.

"In this case, we're protecting against a very serious disease, a common cancer in women," said Dr. Neal A. Halsey, director of the Institute for Vaccine Safety at Johns Hopkins University School of Public Health in Baltimore. "And really, we need to be very grateful for having such a vaccine available."

Mindi Alterman took her 19-year-old daughter to get the first shot when she was home from college over the winter break, and plans to have her 14-year-old vaccinated against HPV at the teenager's annual check-up.

"I feel like we're so fortunate," Alterman said. "My daughter did a book report on polio a couple of years ago, and I read it with her. Even when I was growing up, polio wasn't an issue. We had a vaccine for it."

Life-saving test

Before Dr. George Papanicolaou invented the Pap test in the 1940s, cervical cancer was one of the leading cancer killers of American women. It still is in many parts of the world.

But between the mid-1950s and the early 1990s, the number of U.S. women who died each year from cervical cancer declined by 74 percent. With the Pap test, precancerous cells — or tumors at their earliest stages — could be found and removed before they became life threatening. It surely was one of the major achievements in 20th-century medicine.

In the 1980s, the culprit was found to be human papillomavirus, or HPV. It proved to be incredibly common. Between 50 percent and 70 percent of all adults who have sex are exposed to the virus at some point in their lives.

Although more than 100 subtypes of HPV exist, only a handful cause cervical cancer. Two of them, known by their numbers 16 and 18, cause about 70 percent of all cervical cancers. Two others cause 90 percent of genital warts.

Many times the body clears the virus on its own. But if the virus takes root deep within the lining of the cervix, it can enter healthy cells and hijack their internal controls.

Once inside the cell, the virus's protein coat dissolves, releasing its own genetic material that eventually disables the host cell's ability to stop growing if it becomes cancerous.

The new vaccine contains bits of the virus's own protein coat. It trains the body's immune system to recognize and destroy four subtypes of the virus.

Before the FDA approved the Merck vaccine in June for girls and women ages 9 to 26, four studies that included 21,000 women in several countries were conducted.

It found that if given to women who never had been exposed to HPV, the vaccine was nearly 100 percent effective in preventing infection with those four virus subtypes.

It didn't work very well in women already infected with those viruses. And since HPV is so common, the federal advisory committee on vaccines recommended the shots be administered to girls at 11-12 years, and as young as 9. Before they could be exposed.

Required for school

In Austin, lawmakers are debating whether to overturn Perry's mandate or codify it with new legislation.

A bill written by state Sen. Leticia Van de Putte, D-San Antonio, also would make the vaccine mandatory for entry into sixth grade, but would start this year rather than fall 2008, as the governor's executive order calls for.

"For me it's more of a reimbursement issue," Van de Putte said. "I think that until we have vaccines that are in that (mandatory) regimen, the people who will choose for their daughters to be protected against cervical cancer will probably have to pay it out of pocket."

Insurance coverage for the vaccine is unclear. Last summer, it was added to the federal Vaccines for Children program, which covers children on Medicaid, CHIP, the uninsured and underinsured. State law requires health plans doing business in Texas to cover required childhood immunizations, but only through age 6.

In 2003, Texas made it easier for parents who objected to vaccinating their children to opt out of regulations requiring they be up-to-date on required immunizations before they could go to school. Those with philosophical or religious objections can request a form from the Texas Department of State Health Services, sign and notarize it, and return it to the school for an exemption good for two years.

Under Perry's proposal, opting out would be even easier — parents could get the form online.

Less than 1 percent of Bexar County children are exempted, although a few private schools have rates as high as 4.5 percent. Some fear making the vaccine mandatory for school entry might push that percentage upward.

"The (mandatory vaccination) laws are very helpful for making it clear that this is something endorsed by the public health officials and government, and that helps send a strong message that they are good vaccines," Halsey said. "But I probably would have waited a year to see that the vaccine is going to be delivered and there will be an adequate supply, that we're effectively finding ways to get a high percentage of the kids immunized, and get greater public acceptance."

A different approach

Traditionally, vaccines have been given to children to create what health officials call "herd immunity," to protect populations from spreading diseases among themselves — even if a few aren't immunized.

The HPV vaccine is different in that young children aren't spreading it among themselves through sneezes and casual contact. It's given to protect against the risk of a sexually transmitted disease later in life.

And the fact it's a sexually transmitted disease concerns some parents and family groups, who worry the vaccine will send the wrong message to girls and that making it mandatory will usurp parents' rights — regardless of whether they can fill out a form and opt out.

"We strongly supported the development of this vaccine," said Peter Sprigg, vice president for policy with the Family Research Council in Washington. "But the one area that we draw the line is that we oppose mandatory vaccination for school attendance. We feel that parents are and should be the principal decision makers regarding their children's health and medical care, and there's not sufficient public health justification to override that in this case."

Meanwhile, doctors are glad to finally have a vaccine against cervical cancer, which can strike both young and old.

"The youngest (cervical cancer patient) I've seen is about 17, and I've seen it up to 95," Hall said. "The median age for diagnosis is about 45 — although we're seeing a lot of it in younger women because of sexual activity."

That doesn't necessarily mean promiscuous behavior, Hall added.

"You could have just one partner at age 16 and have cervical cancer by age 20. It's not only the girl's activity but the partner's activity as well, whether they've been exposed to a high-risk virus."