The attendant walked into the hospital waiting room and called my name. I took a deep breath and hurried through the door. “I’m always surprised when my name is pronounced properly at a doctor’s office,” I said.

He chuckled. “You’ve been here before.”

“Yes,” I said. “Today are my five-year scans.”

“You’re a frequent flier!” he said. “Good luck.”

I lay on the bench and slowly slid into the doughnut-shaped machine. As I did, I noticed the ceiling. It was painted with a scene of sunlight peeking through some leafy branches.

For all the cruel randomness and vagaries of cancer, the disease, as a brand, is extremely consistent. There are the recognizable symbols: the bald head, the yellow wristband, the pink ribbon. There are the well-known treatments: chemotherapy, radiation. There are the familiar expressions: Stage IV, metastases, remission, cure. But of all these elements, perhaps none is more enduring than the metric of the five-year survival rate.

When I first learned that I had aggressive bone cancer in my left leg in 2008, I did what many patients do: I immediately searched out the five-year survival figures. I then did the grim calculation of how old my children would be at that time and whether I would outlive my parents. Over a brutal year of chemo, surgery and rehabilitation, I kept an indelible ticking clock in my head. Sometimes I wondered, “Why won’t the clock speed up?” Other times, “Why won’t it slow down?”

And as I slogged through subsequent years of scans — first every three months, then every four, then every six — and experienced what survivors call “scanxiety,” I imagined what the five-year benchmark would feel like. Like an actor practicing my Oscar acceptance speech, I even rehearsed exactly what I would do: break down in tears, give a party, buy plane tickets to Hawaii.

And yet, as I approached the milestone in recent weeks, I began to feel more ambivalence. What happened? Or, had I been wrong all along?

The concept of the five-year survival rate for cancer was introduced in the 1930s. Initially, the designation was used for blood cancers, which grow fast and were extremely lethal at the time, said Dr. Siddhartha Mukherjee, a cancer specialist at Columbia University Medical Center and the author of “The Emperor of All Maladies,” which won a Pulitzer Prize. For those patients, reaching five years was considered something of a miracle. “The idea was you could define a time point where it would make sense to think about that cancer as being cured,” Dr. Mukherjee said. “From there it crept backward into all cancers.”

By the 1950s, five-year survival figures were becoming standard, and by the early 1970s the National Cancer Institute began releasing regular statistics for most forms of the disease. In the face of such authoritative endorsement, the public accepted these figures as meaningful.

But from the very beginning, many scientists were uneasy with grouping all forms of cancer under one metric of survival. “Five years is quite an arbitrary number,” said Julia Rowland, the director of the National Cancer Institute Office of Cancer Survivorship. “For some cancers, if you haven’t had a recurrence in two years, your rate of recurrence drops considerably. For others, like breast cancer, you can have a recurrence at any time.”

For these reasons (and more), Dr. Mukherjee called the five-year figures a “vestige of the past” and predicted that in the near future they would be replaced with more individualized benchmarks. “Just as it makes sense to personalize cancer therapy, it also makes sense to personalize what survival means to an individual patient,” he said. Until then, he considers the five-year survival figure an “instrument of convenience.” In his book he tells the moving story of delivering flowers to a patient when she reached the date. “I was responding to the iconography,” he said. “We mark birthdays, and if you’re a cancer physician you mark survival days.”

Patients, too, mark survival days. Almost everyone I know who’s been told they have the disease can tell you the date. But how to recognize that “cancerversary,” especially the five-year one, is a source of surprising unease. In conversations with nearly two dozen survivors, I found patients divided almost evenly between those who view their five-year “cancerversary” as a joyous occasion and celebrate with gusto, and those who view it as a more solemn day and acknowledge it with quiet gratitude and continued vigilance.

On the joyful side, one breast cancer survivor told me she held a “queen party” at which she decorated a cake in the shape of Queen Elizabeth’s coronation crown and wore a purple ball gown and crown of jewels. Another told me that on her “five-year celebration day,” her husband treated her to lobster tail and crab legs at Red Lobster.

A veteran of testicular cancer told me that when he hit five years, he felt invincible and started running across streets and dropping his surfboard into disproportionately huge waves. “Then I settled down a bit,” he said. “But I still cannot be killed.”

On the more subdued side, one breast cancer survivor who learned she had the disease in her early 30s told me that every year on her “cancerversary” she sends out “a sappy email to all the wonderful people in my life, thanking them for all they’ve done, and continue to do, to make my life so special.” When she hit five years, she asked her doctor what to think.

“Well, five is better than four,” he said, “but six will be even better.” She’s now at eight.

The parents of a boy who was found to have Stage IV neuroblastoma at age 4 told me that when they approached the five-year mark, they planned a party. “But when the time came, we just felt too superstitious about it,” the mother said. “Why tempt fate?” The boy reached the mark of eight and a half years this week, she said, and is healthy and happy.

As for me, when my oncologist announced that my scans were clean (I had reached five years with no sign of cancer), I did a small fist pump but was otherwise more stone-faced and sober than I had anticipated. I spent a few minutes grilling him about ongoing challenges, and he asked me to come back in a year for my next appointment. When I stepped outside, instead of sobbing uncontrollably as I had after previous scans (and instead of buying those tickets to Hawaii), I stood in silent awe at my good fortune. Unlike winning an Oscar, I had done little to earn this moment. I am among the lucky ones, at least for now: My biology had taken the chemistry. Like anyone in this situation, I have met many who never made it this far.

Four years ago, on the first anniversary of the diagnosis of my cancer, I saw my surgeon, John Healy, and asked what message he would give my daughters if I died. He said he would tell them what he has learned treating this disease for decades. “Everybody dies,” he said. “But not everybody lives. I want you to live.”

That has been my motto ever since: to live. If my cancer comes back, I want to have learned that lesson. If it doesn’t I want to have learned it, too. It’s the message I took from one year; I take it today from five years; and I hope to take every year that I slide back into the doughnut hole and look up at the sun peeking out through the leaves.