When imatinib (Gleevec) appeared on the market just over 2 decades ago, it revolutionized the treatment of chronic myelogenous leukemia (CML) and transformed it from a grim diagnosis into a largely treatable form of blood cancer. New generations of tyrosine kinase inhibitors (TKIs) have continued to expand options for patients, and many can look forward to normal lifespans.
But these medications cause side effects and can be expensive. Long-term data doesn’t exist for the newer therapies, so no one knows whether they can harm patients over time. None of this is particularly unusual for medications to treat chronic illness, but now there’s a twist: Over the last few years, physicians have experimented with taking CML patients off TKIs entirely, to see how they fare. So far, the results are promising.
“Our focus has changed because the results of treatment are so good,” hematologist-oncologist Ehab L. Atallah, MD, of the Medical College of Wisconsin, Milwaukee, said in an interview. “We’re trying to get people off their medication.”
Still, research estimates that only 20% of patients with CML will be eligible for treatment discontinuation and benefit from it in the long term. As a result, the wide majority of patients will need to be on drugs indefinitely.
Gleevec: A new age dawns
In the early 1990s, before the era of TKIs, the 5-year relative survival rate from CML was just 27%, and the 10-year rate was only 9.5%, according to a 2008 report. “If someone showed up with CML, their only option was to go to a bone marrow transplant. About half survived the transplant, and half of those had significant complications from it,” Dr. Atallah said. According to him, just about everyone who didn’t get transplantation would go on to die.
Then came Gleevec, which received Food and Drug Administration approval in 2001. It ushered in the era of “targeted” cancer treatment by specifically killing CML cells, instead of relying on traditional chemotherapy’s carpet-bombing approach.
“Gleevec and other TKIs have revolutionized how CML is treated, and patients are now living normal lives,” hematologist-oncologist Catherine Lai, MD, MPH, of the University of Pennsylvania, Philadelphia, said in an interview.
Alan Fahnestock, a 68-year-old retired telecommunications specialist in north-central Washington state, is one of the fortunate patients.
He was diagnosed with CML in 2004 after he underwent a thoracic CT scan in light of his tobacco use. “My GP found something odd in my lungs and referred me to a pulmonologist, who couldn’t figure it out either. He transmitted blood samples to my eventual hematologist/oncologist,” Mr. Fahnestock said in an interview. “It’s not clear to me that anybody ever figured out what the ‘oddity’ was. It has since apparently gone away. But the oncologist ran all the tests and came up with CML.”
Mr. Fahnestock hadn’t noticed any symptoms, although “this is, perhaps, because I tend not to pay a lot of attention to such things, having abused my body fairly severely over the years and having been borderline anemic since I was a kid. I don’t really expect to feel great and am a bit of a fatalist: I just get on with things until I no longer can.”
His physician prescribed Gleevec. “I had no particularly notable side effects, and carried on with my life pretty much as if nothing had happened,” Mr. Fahnestock said. He stayed on the drug for almost 20 years.
CML rooted in chromosome swap
It’s not clear exactly what causes CML, although the Mayo Clinic says most cases are linked to an abnormal, extra-short “Philadelphia chromosome,” created when two chromosomes swap material. This happens after birth.
Mr. Fahnestock thinks he happened to develop a random mutation. He also wonders if his work stints in the former Soviet Union in Vladivostok, “where the Soviet nuclear submarine fleet was decomposing,” and in Kiev, Ukraine, “which is not all that far from Chernobyl,” may be responsible.
Most patients, like Mr. Fahnestock, are men. Males will account for about 5,190 of the cases diagnosed in 2023, according to the American Cancer Society, compared to 3,740 in females.
Mr. Fahnestock’s CML diagnosis came at a fairly young age, when he was in his 40s. The average patient is diagnosed at 64. But it’s not unusual that he experienced no apparent symptoms when the cancer was found. In fact, that’s the norm.
Most patients with the disease – which is diagnosed in about 8,900 patients in the United States each year – are asymptomatic or have mild symptoms, Dr. Lai said. Their disease is discovered when “an elevated white count is found on routine blood work,” she said.
“The other group of patients typically present with very elevated white blood cell counts and splenomegaly with symptoms of fatigue and other constitutional symptoms. When the WBC count is very high, it is important to rule out transformation to accelerated or blast phase and also rule out an acute leukemia.”
Polymerase chain reaction is an especially important test during diagnosis, Dr. Atallah said, since it provides baseline data about the cancer that can be tracked.
TKIs: Mainstay of treatment
Four drugs are FDA approved for initial treatment of CML: imatinib (Gleevec), the second-generation TKIs dasatinib (Sprycel) and the third-generation TKI nilotinib (Tasigna). The third-generation TKIs bosutinib (Bosulif) and ponatinib (Iclusig) are approved for use as first-line treatments for patients who cannot tolerate the other drugs or are resistant to them.
The first-in-class drug asciminib (Scemblix), approved by the FDA in 2021, is a third-line drug for patients who failed treatment with two other TKIs and certain patients with the T315I mutation.
Dr. Lai said that it’s crucial to avoid side effects as much as possible “since the goal is for patients to be compliant and take the pill every day and not miss doses.” In younger patients, “I typically choose a second-generation TKI as my first choice, since there is a higher likelihood of getting into a deep molecular remission more quickly. If treatment-free remission is something a patient is interested in, a second-generation TKI is more likely to make this happen.”
According to Dr. Atallah, about half of patients end up using more than one drug because their initial choices either don’t work or cause intolerable side effects. Nevertheless, Dr. Lai noted: “Overall, patients do extremely well if compliant with their medication.”
Exceptions include the noncompliant and patients with more aggressive disease, like an accelerated or a blast phase, she said. For the latter patients, “allogenic bone marrow transplant should be considered once the patient is in remission.”
In remission, consider drug omission
How should patients be monitored if they are doing well?
“In general, I tend to follow patients monthly for the first six months after starting therapy, to make sure they are tolerating it well and to help manage side effects,” Dr. Lai said. “After that, I follow once every three months, and then often space out visits depending on whether they hit their molecular milestones and how long they’re in remission.”
In certain cases, patients may be taken off medication. The most recent National Comprehensive Cancer Network guidelines for treatment of CML, published in 2021, say that “discontinuation of TKI therapy (with close monitoring) is feasible in carefully selected, consenting patients” with early stage CML who’ve reached remission, defined as deep molecular response (DMR) of at least MR 4.0 for at least 2 years.
The guidelines caution that disease recurrence appears in “approximately 40%-60% of patients who discontinue TKI therapy after achieving DMR experience recurrence within 12 months of treatment cessation, in some cases as early as one month after discontinuation of TKI therapy.”
Still, the guidelines add that “resumption of TKI therapy immediately after recurrence results in the achievement of DMR in almost all patients.”
Dr. Atallah said stopping medication can be especially helpful for patients who grapple with side effects such as fatigue, diarrhea, and muscle aches. Some patients who take the drugs fear losing their health insurance and facing sky-high drug expenses. In 2018, average daily TKI costs for patients with CML were over $350, a 2020 report found.
Many patients were prescribed hugely expensive second-line treatments rather than inexpensive generic imatinib, the report said, despite “no evidence that later-generation TKIs provide superior progression free or overall survival.”
Many patients, however, refuse to consider stopping their medication, Dr. Atallah said. More data about treatment-free remission is needed, and the 21 U.S. academic medical centers in the H. Jean Khoury Cure CML Consortium are gathering information about patient outcomes.
Mr. Fahnestock is a fan of treatment-free remission. He stopped taking Gleevec about 2 years ago on the advice of his physician after he reached undetectable levels of disease.
“It was sort of a nonevent, really, with no discernible physical effects beyond exacerbation of the osteoarthritis in my hands,” he said. According to him, it’s not clear if this effect is linked to his eliminating the medication.
“I also vaguely hoped I’d feel better, even though I’d never been able to nail down any deleterious side effects,” he said. “No such luck, as it happens.”
Blood work has indicated no resurgence of the disease, and Mr. Fahnestock continues to volunteer as a rural firefighter.
“In general, I’m apparently reasonably healthy for my age, despite my folly [in younger years], and firefighting requires me to stay in reasonable shape,” he said. “I’ve recently been made aware of minor kidney issues and prediabetes. But, hell, I’m genetically scheduled to croak within 5 years or so, so why worry?”
National survival statistics in CML vary by factors such as gender and age, as a 2021 study revealed, and men have worse outcomes. Still, there’s a good chance Mr. Fahnestock won’t need to worry about CML ever again.
Dr. Atallah disclosed research support from Novartis and Takeda and has served both of those firms and Bristol-Myers Squibb as a consultant advisor. Dr. Lai discloses tied with Bristol-Myers Squibb, Jazz, Genentech, Novartis, Abbvie, Daiichi Sankyo, Astellas, MacroGenics, Servier, and Taiho. Mr. Fahnestock has no disclosures.
This story originally appeared on MDedge.com, part of the Medscape Professional Network.
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