Not all tumors are the same.

A recent analysis of breast cancer data reveals that many small breast cancers are slow-growing and have an excellent outlook. In fact, many will never cause serious symptoms or require treatment within a patient’s lifetime.

On the other hand, there are fast-growing tumors that can be fatal. They often become a problem before they’re ever detected by mammography.

Now a research team at Yale has shed a light on these tumor differences after analyzing invasive breast cancers. Researchers examined information about cancers diagnosed between 2001 and 2013, which they obtained from the Surveillance, Epidemiology, and End Results (SEER) database.

The data published this month in the New England Journal of Medicine (NEJM) showed that doctors often overdiagnosed or overtreated older patients who had slow-growing tumors, even though those tumors may likely not have been life-threatening.

The study authors wrote that it didn’t matter so much if the breast tumor would eventually progress. Instead it only mattered if it progressed during the patient’s lifetime.

“It is important that we educate physicians, patients, and the public on the indolent, slow-growing nature of some breast cancers,” Dr. Donald R. Lannin, professor of surgery at Yale School of Medicine, and lead author on the paper, said in a press release.

“This knowledge will allow us to individualize treatment options, provide ‘personalized medicine,’ and avoid the major harms of overdiagnosis, which can result in overtreatment and the anxiety and fear that a cancer diagnosis causes,” Lannin said.

The team did not consider noninvasive cancers in this study. Due to different biologic features, the researchers believe more study and a separate analysis is warranted to provide further proof of their results.

Read more: Why more women are choosing double mastectomies »

What is overdiagnosis?

Dr. Doreen Agnese, a surgical oncologist at The Ohio State University Comprehensive Cancer Center, told Healthline that it’s important to define “overdiagnosis.”

“It’s kind of a misnomer. It’s not like these patients don’t really have cancer. They do. The concept of overdiagnosis comes from the fact that some cancers are not really dangerous ones,” she explained.

Standard of care in breast cancer

However, when faced with a specific patient and specific cancer, it can be difficult for doctors to know for certain the best course of action.

The Yale study authors wrote, “Of course, in an individual case it is not yet possible to say with certainty that a cancer is overdiagnosed, so treatment cannot be withheld.”

Dr. Diane M. Radford, staff breast surgical oncologist at Cleveland Clinic, and medical director of the breast program at Cleveland Clinic Hillcrest Hospital, said that statement is true and very telling.

“I think these authors’ findings are provocative,” said Radford. “They conclude that trials may be helpful in the future to identify those groups who could receive less treatment. I don't think they are advocating less treatment now.”

In her experience, patients may choose to delay surgery for their own reasons. In a study that she and others presented at the American Society of Breast Surgeons, they found that almost half of patients had a patient-related factor associated with delays in getting breast cancer surgery.

Their reasons included vacation, work-related issues, family commitments, and additional time needed to consider treatment options.

“I would be more comfortable with a patient delaying treatment who has a small hormone receptor-positive cancer than a patient with a high-grade triple-negative cancer,” said Radford.

She also cautioned that some cancers are so small that they never show up on breast imaging, even MRI. Yet they can present as axillary nodal metastases. “Small,” she said, certainly doesn’t equate with “indolent.”

“I think it would be going out on a limb to say monitor only,” said Radford.

Radford says at this point she relies on the standard of care to ensure her patients have the best possible outcome.

“I offer standard of care per NCCN [National Comprehensive Cancer Network] guidelines or Cleveland Clinic Care Paths,” she continued. If a patient’s health means they cannot receive the recommended standard of care “a multidisciplinary team approach should occur. In general, if a patient refused surgery they should be followed closely with physical exams and regular breast imaging, if they agree to return for follow-up.”

Agnese believes age is an important consideration when debating treatment options.

“In a woman at 70 years old with a small breast cancer, the likelihood is that she will die of something else over the next 20 years,” she explained.

However, she pointed out that nothing is guaranteed in cancer treatment, and that cancers that have a good outlook can still become metastatic.

“It’s not an exact science, as much as we would like it to be,” said Agnese. “To watch and do nothing at all is not currently done. Nobody wants to be the doctor who didn’t treat and then it spreads and leads to death.”

Read more: New drugs targeting cancer 'biomarkers' could revolutionize care »

Monitoring other cancers

“When it comes to breast cancer, this is a very controversial topic,” said Dr. Jack Jacoub, medical oncologist, and director of thoracic oncology at MemorialCare Cancer Institute at Orange Coast Memorial Medical Center in California.

Jacoub pointed out that from a medical oncology standpoint there are many scenarios where they advise individuals to engage in watchful waiting.

“There’s an understanding that early intervention doesn’t necessarily correlate with improved outcomes,” Jacoub said. “And if we intervene now, it probably won’t make a difference in the overall picture, when we consider life span and morbidity.”

He said low-grade lymphoma is the most common scenario where cancer specialists are dealing with this observation option.

“Untreated, it can go many years without harming the patient or shortening the cancer-specific life span. For this type, chemotherapy and other therapies may be extreme,” said Jacoub. “If there are symptoms or it changes to a more aggressive course, we would intervene and the patient hasn’t lost anything.”

However, simply watching and waiting can be difficult for patients to accept.

“There is data, and there is a prevailing opinion in the western world, specifically the United States, that patients often don’t opt for the observation route,” Jacoub said. “It’s hard for patients and their families to accept watchful waiting, particularly younger, healthier individuals.”

According to Jacoub, there’s an abundance of information to support a watchful waiting approach to some types of prostate cancer.

Indeed, a 2016 study published in the NEJM compared active monitoring with surgical treatment called radical prostatectomy and external-beam radiotherapy to see how they affected patients with localized prostate cancer.

The research involved 82,429 men aged 50 to 69 who had a diagnosis of localized prostate cancer. They looked at patient mortality at a median of 10 years at follow-up. In addition, they also looked at secondary outcomes, which included the rates of disease progression, metastases, and deaths from any cause.

The mortality rate from prostate cancer specifically was low, no matter what treatment was given. But surgery and radiotherapy treatments were associated with fewer incidences of disease progression and metastases, when compared to active monitoring.

Read more: Science says get moving to avoid increased risk of certain cancers »

The human element

While some patients want to pursue more treatment than is needed, others prefer waiting and watching.

But when active surveillance is an option, there’s a lot riding on the patient being compliant with doctor’s orders.

Jacoub uses the example of young men with testicular cancer, which is often highly curable, to illustrate the fickle nature of patient compliance.

“In the earlier stage [of disease] you could probably avoid therapy [via chemotherapy or radiation] after surgery to reduce the risk of recurrence,” Jacoub said. “Why give those young men chemotherapy or radiation?”

He continued that if doctors and patients work together they can spot reoccurrence early.

“If it recurred, you could intervene and cure rate would not change,” Jacoub explained. “This surveillance option is appropriate and supported.”

However, this surveillance can be more complicated when the human element comes in.

“Their surveillance schedule should be very strict for up to 10 years,” said Jacoub. “In that age group, patients may go away to school or relocate for work. How likely is it that they’ll follow up? You have to know who you’re dealing with and consider the person’s whole picture.”

In women, deciding to treat breast cancer can be complicated especially since the disease will strike both young and middle-age women. While a woman in her 70s with a slow-growing tumor may be more likely to die of other causes in her lifetime, a young woman with the same tumor may need more invasive treatment to stop the cancer from becoming deadly.

“That should give you pause. This is not an elderly, unwell group,” said Jacoub. “Even if there is an excellent prognosis with, as with early-stage endocrine sensitive breast cancer, it’s not 100 percent.”

Jacoub emphasized that doctors have to take the long view in treating the patient.

“You can have a late recurrence even 20 or 30 years later,” Jacoub explained. “It’s a big problem and can be incurable at that junction. You have to be careful about undertreating.”

Monitoring comes with another set of problems, including stress on the patient and family.

“She’ll need frequent imaging, and the radiologist reading that image will be very critical in scrutinizing it — it’s just not that easy,” Jacoub said. “Even women with benign breast disease will come in having had multiple biopsies and are thinking about having their breasts removed. We don’t advise that, but it’s understandable. Imagine living under that kind of cloud for years.”

If breast cancer does progress, Jacoub says treatment can become a labyrinth of chemotherapy, pills, radiation, and office visits. That risk can make treatments over surveillance look more appealing for doctors and patients.

“There’s a common sense approach,” said Jacoub. “We have to separate the science and the numbers and look at the person. What will it do to their life?”