ORLANDO – Patients who undergo cytotoxic chemotherapy, even in the modern era, are at increased risk for developing myeloid neoplasms, based on data from a cohort of nearly 750,000 adults who were initially treated with chemotherapy and survived at least 1 year after diagnosis.

In the cohort, the standardized incidence ratio (SIR) for treatment-related acute myeloid leukemia (tAML) or myelodysplastic syndrome (MDS) was four times greater than would be expected in the general population, reported Lindsay M. Morton, Ph.D., of the division of cancer epidemiology and genetics at the National Cancer Institute in Bethesda, Md.

“We now demonstrate that there are elevated risks for treatment-related leukemia after treatment for a broad spectrum of first primary malignancies that are generally consistent with what we know about changing treatment practices,” she said at the American Society of Hematology annual meeting.

“The number of cancer survivors in the United States has increased dramatically, to reach nearly 14 million individuals today, and in just the next few years the number is expected to reach more than 18 million people, which means that the long-term health of this population is of great clinical importance as well as public health importance,” Dr. Morton emphasized.

The link between cytotoxic chemotherapy and leukemia risk has been known since the 1960s, with certain classes of agents carrying higher risks than others, including platinum-containing compounds, alkylating agents (for example, cyclophosphamide, melphalan, chlorambucil), topoisomerase II inhibitors (doxorubicin, daunorubicin, epirubicin, etc.), and antimetabolites (5-fluorauracil, capecitabine, gemcitabine, et al.).

Treatment-related leukemias are associated with higher doses of these agents, and the trend in contemporary medicine is to use more of these agents upfront for the treatment of primary malignancies. Yet estimates of the risk of tAML, MDS, or other malignancies have been hard to come by because of the relative rarity of cases and the sporadic reports in the literature, Dr. Morton said.

The investigators previously reported that risk for tAML and other myeloid neoplasms changed over time, and showed that since the 1990s there was an uptick in risk for patients treated with chemotherapy for cancers of bone, joints, and endometrium, and since 2000 for patients treated with chemotherapy for cancers of the esophagus, cervix and prostate.

For example, risks for tAML were higher in the 1970s for patients with ovarian cancer treated with melphalan, a highly leukemogenic agent, but dropped somewhat with the switch to platinum-based agents. Similarly, women with breast cancer had a comparatively high risk with the use of melphalan, a decline in risk with the introduction of cyclophosphamide, and then an increase with the addition of anthracyclines and dose-dense regimens.

Risk update

To get a better idea of the magnitude of risk in the modern era, Dr. Morton and colleagues sifted through Surveillance, Epidemiology, and End Results (SEER) data to identify a cohort of 746,007 adults who were initially treated with chemotherapy and survived for at least 1 year following a diagnosis with a first primary malignancy from 2000 through 2012. They calculated SIRs based on variables that included age, race, sex, malignancy type and treatment period.

They looked at four categories of myeloid neoplasms as defined by World Health Organization criteria: AML/MDS, chronic myeloid leukemia, myeloproliferative neoplasms (MPN) negative for BCR-ABL (Philadelphia-negative), and chronic myelomonocytic leukemia (CMML).

They found that 2,071 patients developed treatment-related AML/MDS, translating into a fourfold incidence compared with the general population (SIR 4.1, 95% confidence interval [CI] 3.9-4.2), 106 were diagnosed with CMML

They also identified novel risk for tAML/MDS after chemotherapy by malignancy (see table).

The investigators found that breast cancer, non-Hodgkin lymphoma, and lung cancer were most commonly associated with tAML/MDS (SIRs 4.1, 7.3, and 4.1, respectively, all significant).

In addition, although the overall numbers of cases were small, the investigators noted “strikingly elevated” risks for cancers of bone (SIR 35.1, CI. 16.9-64.6). testes (15.6, CI, 9.2-24.6), and soft tissue (12.6, CI=7.7-19.4),

Risk for tAML/MD was more modestly elevated for cancers of the brain, ovaries, endometrium, cervix, and prostate, and for Hodgkin lymphoma, chronic lymphocytic leukemia, and multiple myeloma.

Adding radiotherapy to chemotherapy for cancers of the breast, lung, and stomach cancers showed a trend toward heightened tAML/MDS risk, but this was not significant.

An elevated risk for CMML was also seen after chemotherapy for lung cancer (SIR 2.5, CI, 1.3-4.4), breast cancer (1.8, CI, 1.3-2.5), and non-Hodgkin lymphoma (2.1, CI, 1.2-3.4). There was elevated risk for CMML following chemotherapy for breast cancer (3.0, CI. 1.7-5.0) and non-Hodgkin lymphoma (4.2, CI, 2.4-6.9).

There were no increased risks for other myeloproliferative neoplasms after chemotherapy for any first primary cancer, however.

“This reminds us that with new uses of standard agents and introduction of new agents, it’s critical to carefully weigh the risks and benefits of systemic therapy,” Dr. Morton said.

The investigators plan to quantify risks associated with specific drugs and doses, she added.

The study was supported by the National Cancer Institute. Dr. Morton reported no relevant conflicts of interest to disclose.

Chemo quadruples risk for myeloid cancers