Risk and consequences of chemotherapy-induced thrombocytopenia in US clinical practice

Thrombocytopenia, an abnormally low blood platelet count, is a potentially serious and costly complication of myelosuppressive chemotherapy [1, 2]. Chemotherapy-induced thrombocytopenia (CIT) can complicate surgical procedures and can lead to chemotherapy dose delays, dose reductions, or discontinuation, which may result in suboptimal patient outcomes, and CIT increases the likelihood of serious bleeding events, which may result in hospitalization [2‐7]. Currently, there are no drugs approved by the United States (US) Food and Drug Administration for the treatment of CIT, and thus options consist of reducing the intensity of or eliminating the offending treatment, platelet transfusions, or pharmacotherapy, although such options are not without risks and costs [1, 3, 4, 8].

Notwithstanding the potential implications of CIT, little is known about the incidence and consequences of this condition in current US clinical practice. To date, only two studies have evaluated the incidence of CIT using US data sources, and the data employed in these studies are now more than a decade old [2, 4]. Moreover, the study by Hitron et al. was based on a small sample of cancer patients receiving high-risk chemotherapy regimens from a single center, while that by Wu and colleagues was based on an electronic medical records database that did not include important information on characteristics of the study population. In addition, only one study has reported the results of a formal evaluation of the cost of CIT, and this study was based on a sample of 75 patients receiving chemotherapy over 20 years ago [5].

Since the incidence, severity, and duration of CIT varies across patient populations and chemotherapy regimens, and because the treatment of cancer has changed markedly over the past two decades, available evidence may not be reflective of current US clinical practice. The current study was therefore undertaken to evaluate the incidence and consequences of CIT among patients receiving selected myelosuppressive chemotherapy regimens for solid tumors or non-Hodgkin’s lymphoma (NHL) using data from two large healthcare claims repositories. The findings of this research were presented, in part, at the American Society of Clinical Oncology (ASCO) Annual Meeting, June 1–5, 2018 [9].

The two study databases included a total of 643,676 patients aged ≥18 years who received myelosuppressive chemotherapy between January 1, 2011 and December 31, 2015 (Table 1). Among these patients, 332,512 (52%) met all remaining inclusion/exclusion criteria and qualified for inclusion in the source population. From the source population, 215,508 patients also received chemotherapy regimens including an agent of interest—mostly commonly, cyclophosphamide (39%) and carboplatin (28%)—and thus qualified for inclusion in the study population. Mean (SD) age of study population was 57.3 (11.3) years, and 70% were female (Table 2). Common comorbidities included cardiovascular disease (16%), lung disease (16%), and diabetes (15%), and a large percentage of patients had a history of infection (61%) or anemia (21%). Characteristics of patients in subgroups defined in cancer type as well as cancer type and chemotherapy agent (Online Additional file 2: Table S1a-b) and characteristics of chemotherapy regimens and supportive care (Online Additional file 2: Table S2) are reported in Online Additional file 2.

Incidence of CIT during the chemotherapy course was 9.7% (95% CI: 9.6–9.8) among all patients in the study population, and ranged from 6.1% (5.9–6.3) among those receiving a cyclophosphamide-based regimen to 13.5% (12.7–14.3) among patients receiving a gemcitabine-based regimen; CIT incidence among patients receiving regimens including carboplatin was 13.2% (12.9–13.5) (Table 3). Incidence of CIT among all patients was 2.7% (2.6–2.8) in cycle 1, 2.7% (2.6–2.8) in cycle 2, and 2.9% (2.9–3.0) in subsequent cycles. Approximately one-third of CIT episodes were managed in hospital.

For hospital admissions with a principal diagnosis of CIT, mean length of stay was 4.6 (4.4–5.0) days, hospital mortality was 4.7% (2.8–6.6), and mean cost of inpatient care was $36,448 (32,332-41,331) (Table 4). For CIT-related ambulatory encounters, most of which occurred in a physician’s office (45%) or hospital outpatient department (41%), mean cost per encounter was $123 (121–125) for the former and $504 (486–524) for the latter. Across cycles with CIT, irrespective of care setting, mean number of CIT-related admissions was 0.03 (0.03–0.03) per patient-episode, and the mean number of CIT-related ambulatory encounters was 3.7 (3.7–3.8) per patient-episode; the total cost of CIT-related care was $2179 (2029-2329) per patient-episode, comprising $1024 (881–1167) for inpatient care and $1153 (1119-1187) for outpatient care. For purposes of comparison, across cycles without CIT, the cost of selected transfusions, labs, and pharmacotherapy (i.e., services that may have been provided for reasons other than CIT) totaled $271 (265–278) per patient-cycle. Incidence and burden of CIT within subgroups defined on cancer type as well as cancer type and chemotherapy agent are reported in Online Additional file 2 (Online Additional file 2: Table S3a-4b).

Using a retrospective cohort design and data from two large healthcare claims repositories, we undertook an evaluation to better understand the current epidemiology and burden of CIT among persons receiving selected myelosuppressive chemotherapy regimens for solid tumors or NHL in US clinical practice. Our findings indicate that the incidence of CIT during the chemotherapy course is high (~ 10%), especially among patients receiving gemcitabine- or carboplatin-based chemotherapy regimens. Because episodes of CIT were identified based on evidence of thrombocytopenia or bleeding documented during healthcare encounters (and not via laboratory results), we believe our algorithm disproportionately captures more severe cases of disease and thus our estimates may not be reflective of the overall incidence of CIT including all cases, irrespective of disease severity.

Our estimates of CIT incidence are, not surprisingly, generally lower than those previously published, presumably due in large part to differences in case-ascertainment algorithms. In the study by Wu and colleagues, which utilized electronic medical records for patients (n = 47,159) treated in US oncology clinics between 2000 and 2007, CIT incidence—defined as a platelet count < 150 × 10⁹ /L—among all patients was estimated to be 41.4%, ranging from 21.2% among patients receiving taxane-based regimens to 64.2% among patients who received gemcitabine-based regimens [2]. However, when employing the same threshold for CIT as employed in the smaller study published by Hitron et al. (i.e., platelet count < 75 × 10⁹ /L, which along with other evidence, was considered to be clinically significant), overall incidence based on data from Wu et al. was calculated to be 13.8%. This estimate based on data from Wu et al. is comparable to CIT incidence reported by Hitron and colleagues (11.2%), CIT incidence reported in an ex-US study (11.9%, with CIT defined as platelet count < 75 × 10⁹ /L), as well as that reported in the current study [4, 11].

Our findings also indicate that the economic costs of CIT-related care are substantial, averaging $2179 per episode, or $1908 more than cycles without CIT. Notwithstanding differences in study design, study populations, and CIT definitions, our estimate of the cost of CIT-related care is comparable to that reported previously by Elting and colleagues [5]. In their 2003 analysis of 75 patients with a solid tumor or lymphoma who developed thrombocytopenia during chemotherapy treatment, mean incremental cost of CIT was estimated to be $1037 in 1999US$, or $2011 in 2016US$. Among our 27,913 cycles with evidence of CIT, 75% (n = 20,920) had evidence of bleeding, and CIT-related costs in these cycles were substantially higher than in the 25% (n = 6993) of cycles without evidence of bleeding. In cycles with bleeding, mean costs of CIT-related care (per patient-episode) totaled $2632, including $1349 for CIT-related hospital admissions and $1281 for CIT-related ambulatory care; corresponding values for cycles without bleeding were $823 (total), $51 (hospital), and $770 (ambulatory).

We note several potential biases vis-à-vis patient (treatment) selection and outcome assessment that may impact the findings of this study as well as important limitations. The accuracy of the algorithm for identifying patients receiving chemotherapy for solid tumors and NHL is unknown, as it has not been validated. However, similar algorithms for identifying cancer chemotherapy patients in healthcare claims databases have been employed in several previously published studies [12‐14]. Because a diagnosis code for CIT does not exist, and the study database does not include results of laboratory tests (i.e., platelet counts), an algorithm based on diagnosis codes for thrombocytopenia and bleeding, and procedure codes for bleeding treatment, platelet transfusion, and TPO-RA therapy, was employed to identify CIT. While the accuracy of this algorithm is unknown, we suspect—as noted above—that patients with less severe CIT may be disproportionately under-represented, and thus the estimated cost of CIT-related care must be interpreted accordingly. We also note that because thrombocytopenia, neutropenia, and anemia are all known hematological toxicities of myelosuppressive chemotherapy, the reported incremental cost of CIT may be, to some extent, confounded by the presence of anemia and/or neutropenia, and the impact of such bias is unknown. Algorithms and variables employed to identify chronic comorbidities and acute illnesses have not been validated, and their accuracy is unknown; also, some patients may be misclassified in terms of their characteristics because healthcare claims are available only during the study period. Data on hospital discharge disposition were available only in the MarketScan Database, and thus were assumed to be generalizable to the overall population of patients hospitalized for CIT. Health plans contributing claims data to the two study databases are different. However, patients may be insured by more than one health plan at the same time, and thus their healthcare claims may be included in both of the study databases; the magnitude of overlap is believed to be negligible. Finally, caution is warranted in generalizing results beyond this evaluation as the study population was disproportionately represented by non-elderly patients with commercial healthcare coverage.

In conclusion, in this retrospective evaluation of cancer chemotherapy patients, CIT incidence was high, especially among patients receiving gemcitabine-based regimens, and the costs of CIT-related care were substantial. Accordingly, interventions aimed at identifying and targeting patients at high risk of CIT for preventative measures may yield substantial clinical and economic benefits.