“We went almost 3 decades with nothing, then all of a sudden we’ve had nine approvals in 5 or 6 years,” said Harvard Medical School, Boston, leukemia specialist Amir Fathi, MD, in an interview. “We’ve had a lot of advancement and a number of good options emerge.”
However, Dr. Fathi and other hematologists cautioned that the treatment landscape is becoming more complex to navigate. And they noted that prognoses for many older patients with AML remain grim. The expensive new treatments may only extend their lifespans by a matter of months, although some are surviving for years.
As the specialists explained, there are a variety of reasons why AML is especially difficult to treat.
“AML is one of the fastest growing human cancers, with tumor cell doubling times measured in mere hours in some patients. Therefore patients can present critically ill with white blood cell counts in the [hundreds of thousands of white blood cells per microliter instead of the normal range of 4,000-11,000]," said leukemia specialist Eunice S. Wang, MD, of Roswell Park Comprehensive Cancer Center in Buffalo, N.Y. “Because blood cells are found in every organ of the body, the sheer volume of rapidly growing cancer cells can overwhelm multiple organ systems in a very short amount of time. These rapid growing cells and the fact that the median age of diagnosis with AML is 67-70 years old makes this a clinically challenging cancer to treat. Chemotherapy strong enough to kill cancer cells run the risk of also harming the patient as well.”
Also, older patients often have comorbidities, and they face risks of infection from both the disease and its treatments, said AML specialist Nicole R. Grieselhuber, MD, PhD, of the Ohio State University, Columbus, in an interview.
Enter targeted therapy, which “has allowed individuals who previously were not candidates for cytotoxic chemotherapy because of their age or possible toxicities to receive effective therapy for AML,” Dr. Wang said. “Therapy directed at specific biological features of AML cells such as mutations (FLT3, IDH1, IDH2) or surface proteins (CD33) can augment the efficacy of conventional chemotherapy or in some cases (i.e., FLT3 inhibitors) be more effective than chemotherapy in controlling AML.”
Targeted therapy drugs “are expected to more selectively kill cancer cells and spare normal counterparts,” she added.
The FDA has approved nine targeted therapy drugs for AML in the last few years.
Retinoic acid and arsenic trioxide therapy for acute promyelocytic leukemia “has transformed this AML subtype into one of the most curable AML diseases,” Dr. Wang said. A 2017 long-term analysis of the drug combination found that complete remission was reached in 96% of 54 high-risk patients and 133 low-risk patients; the 5-year survival rate was 88%. (Some patients also received gemtuzumab ozogamicin, a CD33 antibody-drug conjugate.)
According to Dr. Wang, three FLT3 inhibitors have been approved for AML with the FLT3 mutation: midostaurin and quizartinib in the frontline setting in conjunction with intensive chemotherapy and gilteritinib for relapsed/refractory FLT3-mutant AML.
A 2017 study linked midostaurin plus chemotherapy to longer survival (hazard ratio for death = 0.78; P = .009), versus placebo plus chemotherapy, in patients aged 18-59. This year, a phase 3 randomized trial of quizartinib versus placebo linked the drug to longer survival median overall (31.9 months versus 15.1 months; P = .032) In a 2019 trial, patients who took gilteritinib had longer median overall survival (9.3 months versus 5.6 months; HR for death = 0.64; P < .001).
The success of these treatments “has led FLT3 mutant AML to be reclassified from a poor risk AML subtype to intermediate risk AML,” Dr. Wang said.
A 2022 report about FLT3 inhibitors cautioned, however, that “several drug resistance mechanisms have been identified” and added that “the benefit of FLT3 inhibitor maintenance therapy, either post chemotherapy or post transplant, remains controversial, although several studies are ongoing.”
Gemtuzumab ozogamicin is a monoclonal antibody connected to a chemotherapy drug, according to the American Cancer Society. “The addition of gemtuzumab ozogamicin to intensive chemotherapy has enhanced outcomes of favorable and intermediate risk disease,” Dr. Wang said.
Ivosidenib, olutasidenib, and enasidenib target the IDH1 or IDH2 genes in ADL. “These drugs seem to work by helping the leukemia cells mature (differentiate) into more normal cells,” according to the American Cancer Society. “Because of this, they are sometimes referred to as differentiation agents.”
In older adults, a combination treatment with venetoclax, a BCL-2 inhibitor, and a hypomethylating agent has become standard, Ohio State’s Dr. Grieselhuber said. The treatment is FDA approved.
There are caveats to targeted therapy in AML. The treatments can be enormously expensive, “and even patients with insurance are often shocked by the copay,” Dr. Grieselhuber said. It helps to work with pharmacists, social workers, or nurse navigators to help patients afford the treatments, she said.
Side effects vary by therapy and can include QT elongation and differentiation syndrome.
Most challenging of all, many AML patients still face shortened lifespans even if new treatments are available for them.
“Typically for older patients with AML, the lifespan of patients with therapy was 5-7 months and without therapy was 2-3 months,” Dr. Wang said. “Now, with regimens specifically designed for elderly and/or unfit subjects, many individuals are now routinely living more than a year: 14-18 months to 3-4 years.”
But “the vast majority of AML patients will still die of their disease with overall 5-year outcomes still less than 30% in all age categories,” she said. In addition, “fewer than 50% of AML patients are eligible for treatment with FDA-approved targeted therapies, as their disease biology does not express the mutation or protein needed for efficacy.”
Still, she said, “this represents a vast improvement.” And, she added, “in younger individuals, the combination of chemotherapy followed by allogeneic transplant has now permitted more of these individuals to be cured of their disease.” Dr. Grieselhuber noted that transplants are now considered appropriate even for patients in their 60s or early 70s, and they can be combined with targeted therapy.
Dr. Grieselhuber urged colleagues to keep in mind that quality-of-life preferences will play a role in some patient choices. For example, a elderly patient may reject burdensome infusion therapy and choose a pill instead, even if it has less efficacy. “There’s really no one-size-fits-all,” she said.
And, she added, it can be difficult to make choices about treatment because of the lack of randomized, head-to-head data regarding new therapies.
What’s on the horizon? Dr. Wang highlighted a novel class of targeted therapies called menin inhibitors for patients with NPM1-mutated AML, which she said accounts for one-third of patients with the disease. A treatment targeting disease in the 5%-10% patients with the KMT2A gene is also in the works, she said.
For now, Dr. Wang said it’s essential for clinicians “to perform timely comprehensive molecular and genomic tests on all AML patients at diagnosis and relapse to determine which individuals would benefit from targeted therapy versus cytotoxic chemotherapy. And participation in clinical trials at every stage of AML therapy can help accelerate clinical development of new agents for this disease.”
Dr. Fathi discloses relationships with Daiichi Sankyo, Pfizer, Rigel, Autolus, Amgen, Servier, Takeda, Orum, Menarini, Remix, AbbVie, Astellas, BMS, Ibsen, Gilead, Genentech, and AstraZeneca. Dr. Wang discloses ties with AbbVie, Astellas, BMS, CTI Biopharma, Daiichi Sankyo, Gilead, GSK, Johnson & Johnson, Kite, Kura, Novartis, Pfizer, Rigel, Sellas, and Sumitomo Pharma. Dr. Grieselhuber has no disclosures.
