There was another issue: The whole idea of chemotherapy freaks Becca out. To an adolescent or teenage cancer patient, the benefits of chemo can seem rather abstract while the possible side effects -- hair loss, nausea and mouth sores -- seem anything but.

"Chemo sucks," she said.

On her 16th birthday, Rebecca's family walks along the beach north of Ocean City, Md.
James A. Parcell--The Washington Post

Standard chemotherapy tends to be ineffective against most brain tumors, because such drugs cannot easily get across the blood-brain barrier, the ability of blood vessels to keep toxic chemicals from leaking out of the bloodstream into the brain.

Before coming to a decision, the Lillys needed one more piece of information: an up-to-date brain scan. It showed a slight increase in the size of the tumor since her surgery in May. But the cancer did not appear out of control.

"You learn to expect bad news," Maureen Lilly said. "You're braced to hear it's doubled in size. It's kind of like the good news is there's no bad news."

A

fter the scan, Joe and Maureen Lilly talked it over one more time and made the decision they had been leaning toward: phenylacetate. Becca would start treatment the week after her birthday, as soon as they got back from Ocean City.

The plan was to try phenylacetate for 28 days and then see how she was doing. After a couple of weeks off, if neither the tumor nor the side effects were out of control, she'd start another round.

Even though Packer told the Lillys he would back either choice for Becca, they could tell that his own hunch would have gone the other way, toward RMP-7. That made them uneasy, for he was the doctor who knew Becca best, and they trusted his judgment and had always followed his lead.

"We may be wrong from a medical point of view, but I feel like this is right for Rebecca and what's going on right now in our family," Maureen Lilly said.

As a doctor who has treated hundreds of children with chemotherapy, Packer knows that while its side effects are not pleasant, many children tolerate it quite well. But given that avoiding the side effects of chemotherapy was "at the top of the list" for the Lillys, he said, phenylacetate was "absolutely the right choice for now."

Besides, they could change their minds if the phenylacetate didn't work or its side effects proved too great. If the tumor continued to grow, they might even reconsider RMP-7/carboplatin.

The fear of pain was as bad as the actual hurt -- or worse.

If, however, the phenylacetate could somehow stabilize her tumor and slow its growth, that might allow more time for other experimental treatments to become available. "The family is very smart about this," Packer said. "They know this may buy some time."

The drug drips from a pint-sized plastic bag into a tube that enters Becca's bloodstream directly through a tiny incision above her breastbone and threads through a large vein to the entrance to her heart. A portable battery-operated pump the size of a Walkman keeps the drug flowing steadily around the clock, one bag a day. She carries the pump in a little canvas pack wherever she goes.

Technically, it's a form of chemotherapy, but as far as Becca is concerned, it isn't chemo at all. She has a point. The phenylacetate is a super-concentrated form of a substance that occurs naturally in animals and humans. The dose she receives is about 1,000 times as potent as the natural form.

Most anti-cancer drugs are toxic chemicals designed to kill fast-growing cancer cells. Many also affect fast-growing healthy cells -- such as those in the intestines, mouth and hair. That is why chemotherapy can cause temporary nausea, mouth sores and hair loss.

Because phenylacetate is derived from an amino acid, a building block of proteins that are necessary to all life, it is less toxic than standard chemo. In laboratory tests on animal tumors, phenylacetate also seems to make some cancer cells mature faster and grow old before their time. Theoretically, that could stop them from dividing and multiplying out of control.

W

hen the medical team at NIH explained the phenylacetate protocol to Becca, she was interested less in such theory than in practical details.

Phenylacetate is called a maturing agent, social worker Barbara Beall told Becca. "It somehow causes cancer cells to grow up and stop dividing."

"What do you mean?" Becca asked.

"They get old," Maureen Lilly said.

"Just like me and Mom," Joe Lilly interjected. "We get old and don't have any more kids."

The idea was "to stop the tumor from growing and wait until we see what else can be used to kill it," her father added. "This is not going to make it disappear."

They explained that while it didn't have the usual toxic effects of chemotherapy, she would have to be on an IV for 28 days in a row.

Becca sat quietly in her Camp Funshine T-shirt and her Bugs Bunny cap, with her chin on her left hand, mulling.

"So I'd never be able to swim?" she said. She was sniffling.

Swimming would be taboo while the IV was running, they told her.

"How long will I have it?" Becca asked.

"Till the cancer goes away, Becca," her dad said.

B

ecca stayed quiet. "How will I wear shirts?" she said finally.

"Just like you do now," her mom assured her. The catheter in her chest wouldn't show, except in a bathing suit, and they could go shopping for a new one with a higher cut.

Becca stared down at the pamphlet in front of her. She started to cry, moving her left hand up to cover her face. Her Bugs Bunny cap fell to the floor. Maureen Lilly leaned over and put an arm around her.

"You can make plans, but you're never sure you're actually going to get to that point."

"What upset you, Becca?"

"Not being able to swim."

The Lillys had noticed last spring that Becca reacted more and more to anticipated pain. The fear of pain was as bad as the actual hurt -- or worse. At the dentist's, she got so upset at the prospect of having a small cavity filled that her mom had to take her home. During the meningitis scare, she handled the first spinal tap like a trouper, but the mere mention of another one last month brought tears. Sometimes they had to give her Valium when her IVs broke down and they searched for another vein.

Her dad in particular, the ex-football coach, instilled in Becca the importance of positive thinking. What was the use of fretting about the future -- especially when she was feeling pretty good right now?

"Just pretend you're on the beach, with waves breaking," he would tell her when she cringed in anticipation of another needle stick. "Don't start thinking now about how it's going to hurt later," he advised as a spinal tap was scheduled. "What it does, it'll do. It doesn't hurt now. So wait until it happens."

"And then scream real loud if you need to," added Maureen Lilly.

T

he last time the Lillys had put money down on a beach house was in 1991. That was the summer Becca's tumor was diagnosed, and they never made it to the shore. Five years later, they had finally gotten up the courage to try again, and they were determined to get to the beach this time.

"You can make plans," Maureen Lilly said, "but you're never sure you're actually going to get to that point."

This time they made it. They arrived in Ocean City a few hours after Hurricane Bertha blew through and spent a welcome unmedical week: no IVs, no scans, no stitches, no waiting rooms.

There were still reminders. The day before Becca's birthday (the family celebrated her actual birthday at the beach, a few days before the surprise party), it was hot with no breeze, even by the ocean. The fierce, shimmering glare overwhelmed her. Becca was wading in the surf with her brother, Joe, when the beach began to wobble and she started seeing double. They took her back to the apartment, where she napped for two hours and woke up refreshed.

That evening they cruised the boardwalk. She bought a T-shirt and a toe ring. With her brother, she even went on a series of carnival rides: not just Bumper Cars and Teacups, but Wipeout and the double Ferris wheel. (She drew the line at the roller coaster.)

By the time she got up the next morning, the place was full of balloons and the ceiling fan festooned with crepe paper. On the kitchen counter was a chocolate cake decorated by her brother.

A

fter a leisurely morning at the beach, they went out for fried shrimp, Becca's choice for her birthday lunch. Later, the family headed to the mall, where Becca could pick out an iron-on decal for her new sweatshirt and -- this was the big one -- check out the puppies at the pet store down the block.

Joe let her in on a family secret: Their parents had signed off on the purchase of a dog. There were a couple of conditions, he told her. It couldn't be yippy or huge, and although Becca could pick the name, she had to accept suggestions.

The party was winding down, and so was she. There would be time later to open the gifts and page through the scrap book her sister Anne Marie had arranged for the crowd of guests to put together: a fat bundle of snapshots, cards and scribbled wishes.

"Happy Sweet Sixteen!" wrote Anne Marie's college roommate, Shannon Masson. "We haven't really known each other very long, but one thing I've noticed about you is that your personality really brings out the best in people and maybe causes them to look at things a little differently. . . .

"That's a special gift -- don't ever lose it. . . . Don't ever change."

But for now, Becca was pooped. She hadn't even tasted her own birthday cake.

"I have to go back to NIH," she said to her mom.

The new treatment would begin in the morning.