Treatment outcomes for newly diagnosed, treatment-naïve TP53-mutated acute myeloid leukemia: a systematic review and meta-analysis

Acute myeloid leukemia (AML) is a hematologic malignancy that develops from clonal expansion of myeloid precursors residing in the bone marrow [1]. In patients with AML, leukemic blasts infiltrate the bone marrow and disrupt normal hematopoiesis. AML typically occurs in adults aged more than 45 years; the median age at diagnosis is 68 years. In 2021, there were an estimated 20,240 new cases of AML in the United States [2]. Based on the latest available data (2011–2017), the estimated 5-year survival rate of all patients with AML was 29.5%. A mainstay of AML treatment has been the combination of cytarabine and an anthracycline, e.g., “7 + 3” and “FLAG-Ida” (fludarabine, cytarabine, idarubicin, and granulocyte colony stimulating factor) regimens as intensive induction chemotherapy [3, 4]. For patients unable to tolerate intensive chemotherapy (IC), hypomethylating agents (HMA) are frequently used to treat AML. Since the approval of the oral BCL-2 inhibitor venetoclax (VEN) [5], which demonstrated improved response rates in the Phase 3 registration study, VIALE-A [6], an HMA (e.g., azacitidine [AZA] or decitabine [DEC]) is frequently combined with VEN for the frontline treatment of AML, particularly for patients aged 75 or more years or those unable to tolerate IC [6].

A subset of the AML patient population is characterized by mutations in the TP53 gene, which encodes a transcription factor (p53) that serves as a critical tumor suppressor [7]. Stress, such as damage to DNA, activation of oncogenes, and depletion of ribonucleotides, triggers activation of p53, which then regulates expression of various genes required for DNA repair, cell differentiation, cell cycle arrest, and apoptosis. Most mutations are missense alterations that occur in the DNA-binding domain and often result in decreased or absent DNA binding [7, 8], but in some cases, the mutations can result in a mutated p53 that exerts dominant-negative influence on residual wild-type p53 [8]. Mutated TP53 (TP53m) has been detected in 5–15% of patients with de novo AML [9, 10] and 17.6% of those with secondary AML [11]. Among patients with therapy-related AML, this mutation is detected in about 30% of cases [12]. In addition, TP53m is associated with low blast counts, complex karyotypes, and underrepresentation of concurrent FLT3, RAS, NPM1, and RUNX1 mutations [9].

AML patients with TP53m have significantly poorer prognosis and lower overall survival (6.5 vs. 33.6 months) compared to TP53 wild-type AML patients due to resistance to standard AML therapies [13]; worse outcomes have been reported for TP53m patients compared to TP53 wild-type patients following treatment with IC or low-intensity chemotherapy [9]. Even with recently approved HMA + VEN–based therapies, the median overall survival (OS) remains low at only 5 to 6 months, despite encouraging complete remission (CR)/incomplete hematologic recovery (CRi) rates of 40–60% [14‐16]. Optimal treatment for the subpopulation of patients with TP53m AML has not been established. A thorough understanding of therapy-specific clinical outcomes over the past several decades may help elucidate the magnitude of unmet therapeutic need in this patient population and establish historic expectations for novel therapies and combinations being developed in this space. This systematic review and meta-analysis aims to evaluate outcomes associated with IC, HMA, and VEN + HMA in newly diagnosed, treatment-naïve TP53m AML.

This systematic literature review and meta-analysis was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [17].

This comprehensive and most recent systematic review and meta-analysis was undertaken to evaluate outcomes associated with IC, HMA, and VEN + HMA treatments of newly diagnosed, treatment-naïve patients with TP53m AML. Findings from this study confirm that patients with TP53m AML experience poor outcomes regardless of the type of therapy received. CR rates ranged between 13 and 43% for treatments across studies in the pooled data analysis, whereas CR/CRi rates tended to be between 13 and 49% among the studies that reported such results. CR and CR/CRi rates were better among IC- and VEN + HMA–treated patients compared with HMA alone, but they were still low in comparison to the CR rate of 85% previously reported in TP53 wild-type AML [13, 37, 41]. IC reported the highest pooled CR/CRi and CR rates (46% and 43%, respectively). However, this may represent a selection bias wherein younger and fitter patients who are often more likely to progress to allogeneic stem cell transplantation were historically selected for IC, even in the TP53m setting. With VEN + HMA, the pooled CR rate was only 33% but was higher than the CR rate of 21% for HMA alone.

Median OS estimates for each treatment type were uniformly low, ranging from 6.1 months in the HMA cohort to 6.2 months in the HMA + VEN cohort to 6.5 months for IC. Despite the better CR and CR/CRi rates among IC- and VEN + HMA–treated patients, the pooled median OS of each was similar to that of HMA alone, and all were < 7.0 months, suggesting that improved treatment responses with IC and VEN + HMA did not translate to improved OS.

p53 is key to apoptosis resulting from cytotoxic chemotherapy; therefore, mutated p53 can result in resistance to DNA-damaging chemotherapies that are used to treat AML [7]. Additionally, preclinical studies have shown that p53 loss-of-function in isogenic human AML cell lines results in resistance to HMA treatment with or without VEN [42]. This potentially contributes to the lower rates of CR and CR/CRi and the reduced OS observed in this extremely difficult-to-treat population. Furthermore, TP53m patients tend to have greater degrees of myelosuppression and higher early mortality, with reported early (60-day) mortality rates as high as 26% in a contemporary study at MD Anderson Cancer Center that treated TP53m patients with HMA + VEN, compared with 60-day mortality rates of 4% in non-TP53m patients treated with HMA + VEN at the same institution [14]. Novel therapies that directly target pathways other than those involving p53 are being aggressively evaluated to improve clinical outcomes of patients with newly diagnosed, treatment-naïve TP53m AML [7].

Possible new therapies for TP53m AML include immunotherapy, such as bispecific antibodies, chimeric receptor antigen (CAR) T-cell therapy, and monoclonal antibodies [7]. Immunotherapies that facilitate effector T-cell responses have been used widely to treat other types of malignancies and are now being investigated as treatments for AML [43]. These adaptive immune checkpoint inhibitors alone or in combination with induction chemotherapy or HMA are being evaluated in various subtypes of AML including in TP53m AML [44]. Early studies of bispecific antibodies and CAR T-cell therapy have suggested each therapeutic modality has promise, but a disadvantage of both approaches is the need to target specific antigens, which is challenging in AML, as antigen expression on AML cells is not as specifically or differentially expressed compared to other hematologic malignancy types [7].

Magrolimab is a monoclonal antibody specific for CD47, a leukemic stem cell marker and the ligand for a macrophage immune checkpoint molecule called signal regulatory protein alpha (SIRPα) [45, 46]. By binding SIRPα, CD47 triggers a signal transduction cascade that results in a “don’t eat me” signal communicated from the malignant cell to the macrophage [45, 46]. Phase 1b/2 studies are investigating the efficacy and safety of magrolimab in combination with AZA, which synergizes with magrolimab by inducing the “eat me” signals on leukemic cells, and in combination with AZA + VEN in AML [45]. In the Phase 1b study of magrolimab in combination with AZA, ORR among patients with TP53m AML (n = 72) was 48.6% (33.3% CR, 8.3% CRi, and 5.6% PR), and median OS was 10.8 months [47]. This median OS is encouraging when reviewed in context of the OS with IC, VEN + HMA, or HMA alone as shown in this paper, with median OS ranging from 6.1 to 6.5 months with these modalities. A Phase 3 trial (NCT04778397) comparing the efficacy and safety of magrolimab + AZA with that of VEN + AZA or IC in adult patients with newly diagnosed TP53m AML is ongoing [48].

Another compound in development for TP53m AML is eprenetapopt, a novel, first-in-class, small molecule that induces TP53m cell apoptosis. Eprenetapopt in combination with AZA showed promise in a Phase 1b/2 trial of TP53m myelodysplastic syndrome and AML patients [49, 50]. As a result, a Phase 1 trial of eprenetapopt + AZA + VEN was initiated. This study reported encouraging early efficacy data and is ongoing [51].

A regimen of 10-day DEC showed favorable clinical responses (including CR/CRi) among patients with TP53m compared to patients with wild-type TP53 in a single institution trial [52]; however, this was not reproduced in a randomized Phase 2 study comparing 5-day versus 10-day DEC [21].

This systematic review and meta-analysis provides insight and establishes clinical outcome benchmarks using contemporary literature and therapies in patients with TP53m AML receiving different types of therapies. While patient and treatment selection criteria limited the number of articles included in this study, strict inclusion and exclusion criteria were added to optimize the validity of the findings. The results of the full-text screening were cross-referenced with published systematic literature reviews on similar topics to ensure the inclusion of all relevant publications. The scope of the review was broad, encompassing RCTs, nonrandomized or single-arm trials, and prospective or retrospective observational studies. The Risk of Bias 2 tool and the Newcastle–Ottawa scale were used to assess the strength of evidence available for each outcome in the context of AML research. However, a limitation of this analysis, as with similar systematic reviews and meta-analyses, is that the analyses for all outcomes were based on the pooling of proportions from each intervention group, rather than comparative evidence. Due to the limited number of available studies and the lack of details about outcomes of specific intensive or nonintensive regimens, we were unable to compare outcomes between individual treatment regimens. This represents an important topic for future study of TP53m AML, as it is possible that outcomes could differ based on the specific intensive or nonintensive regimen applied. Additionally, we were unable to make reliable comparisons between treatment regimens within age subgroups owing to the greater likelihood that older patients received HMA or VEN + HMA over IC. It is also important to note that each study enrolled different patient populations using different eligibility criteria, and each study was conducted over different time periods. These factors most likely impacted both response and survival outcomes. Consequently, it must be clearly highlighted that it was not the intent of this analysis to draw conclusions or to infer the relative effectiveness of these interventions compared to each other or to other treatments. Furthermore, this analysis did not explore methods of controlling for heterogeneity other than stratification through study design.

Estimates of CR, median OS, and other measures of efficacy were low across treatments, including IC, HMA, and VEN + HMA, for patients with newly diagnosed, treatment-naïve TP53m AML. Though adding VEN to HMA improved CR and CR/CRi rates compared with HMA alone, median OS was not prolonged. Median OS remained dismal at 6.1, 6.2, and 6.5 months for HMA alone, VEN + HMA, and IC, respectively, highlighting the dire unmet need in this population of myeloid malignancies. Findings from this study point to a substantial need for new therapies that can effectively treat newly diagnosed, treatment-naïve TP53m AML and improve outcomes.