The clinical data of 26 older patients with AML who received the azacitidine and venetoclax regimen at Yuyao People's Hospital (Yuyao, China) between January 2021 and May 2023 were retrospectively analysed. All patients were diagnosed based on bone marrow cell morphology, flow cytometry typing, cytogenetics and molecular biology typing criteria. Prognostic risk stratification was performed according to the National Comprehensive Cancer Network 2021 3rd Edition criteria (10). Relevant patient data were collected and followed up. Owing to various reasons such as age, financial situation and physical condition, none of the enrolled patients were eligible for conventional chemotherapy. The inclusion criteria were as follows: i) ≥75 years old or 65–75 years old with an Eastern Cooperative Oncology Group physical fitness score of 2–4 (11); ii) presence of severe heart, lung, liver and kidney diseases; and iii) presence of any comorbidities deemed unsuitable for intensive chemotherapy by the treating physician (4). The exclusion criteria were as follows: i) Previous treatment with methylated drug decitabine or azacitidine and chemotherapy (except hydroxyurea); and ii) presence of other malignant tumours. The present study was approved by the Ethics Committee of Yuyao People's Hospital (Yuyao, China), and all patients or their legal guardians provided written informed consent.

According to the patient's wishes, the treatment was started after excluding chemotherapy connexion. The specific dosage for each regimen was as follows: i) Regimen 1, subcutaneous injection of 100 mg azacitidine on days 1–5 and 100 mg oral venetoclax on days 3–16; and ii) regimen 2, subcutaneous injection of 100 mg azacitidine on days 1–5 and 100 mg oral venetoclax on day 3 plus 200 mg oral venetoclax on days 4–30. The administration was scheduled to be repeated once every 28 days, with an appropriate extension of time if the patient did not recover haematopoietic function [recovery considered as a platelet (PLT) count of >1×10¹¹/l and an absolute neutrophil count (ANC) of >1×10⁹/l].

Bone marrow examination was performed at the end of every course. According to haematologic diagnosis and therapeutic efficacy criteria (10), complete response (CR) was defined as the disappearance of AML symptoms and signs, ANC value in peripheral blood ≥1.5×10⁹ cells/l, PLT count ≥100×10⁹ cells/l, leukocyte classification without leukaemia cells, bone marrow image showing granulocyte type I + II ≤5% and no extramedullary leukaemia invasion. CR with incomplete haematological recovery (CRi) occurred when all the criteria for CR were met except for neutropenia (<1.0×10⁹ cells/l) or thrombocytopenia (<100×10⁹ cells/l). Partial response (PR) was characterized by bone marrow granulocyte type I + II >5% but ≤20%, with one clinical and haematologic response not meeting the CR standard. No response (NR) was defined as bone marrow and blood images not meeting the aforementioned criteria. Finally, overall response (OR) was calculated as follows: OR=CR + PR.

Adverse event severity was graded following the National Cancer Institute Common Adverse Event Evaluation Criteria version 5.0 (12). The patients' blood, liver and kidney functions were regularly monitored during treatment. When the patient's ANC was <1.0×10⁹ cells/l, patients were administered subcutaneous injections of granulocyte colony-stimulating factor (range, 200–400) µg/day. When the patient's haemoglobin level was <60 g/l, a red blood cell suspension was transfused. PLTs were injected when the patient's PLT was <20×10⁹ cells/l; coinfected patients were treated with active anti-infection treatment (antibiotics). If the patient was co-infected with a fungal infection, CYP3A inhibitors were not used to avoid increasing the venetoclax concentration. Nausea, vomiting, diarrhoea and other gastrointestinal reactions were actively managed with symptomatic treatments.

Patients were followed up until December 2023, mainly through in-patient and out-patient assessments, and telephone follow-ups. The follow-up is part of the standard procedure after treatment.

The results were analysed using SPSS (version 26; IBM Corp.). Categorical variables are presented as proportions, whereas continuous variables are presented as medians (P25, P75). The Kaplan-Meier method was used to analyze OS and progression-free survival (PFS), with the log-rank test used to assess statistical associations, and P<0.05 was considered to indicate a statistically significant difference.

Overall, 26 patients diagnosed with AML were included in the present study. In the all-comers cohort, the median age at diagnosis was 73 years, including 11 patients aged ≥75 years. The median ratio of original cells was 60% (range, 21–97%), and the median treatment cycle was seven (range, 1–18 cycles). A total of 13 patients underwent genetic testing of bone marrow samples, using next-generation sequencing for 278 genes associated with leukemia, as performed by ADICON Medical Laboratory. In European Leukemia Network (ELN) risk stratification, five cases had a good prognosis, 13 cases had a moderate prognosis and eight cases had a poor prognosis. The clinical characteristics of both patient groups are presented in Table I.

At the end of the first treatment course (29 days after the beginning of chemotherapy), 17 (65.4%), five (19.2%) and three (11.5%) cases achieved CR, CRi and PR, respectively. The CR + CRi rate was 84.6%, and the objective response rate (ORR) was 96.2% (Table II).

The median number of sessions for all patients was seven (range, 1–18 sessions). Of the 26 patients, nine (34.6%) patients relapsed within a mean of 6.7 months (range, 4.7–14.1 months). Two patients did not undergo the second phase of chemotherapy owing to their critical condition, and one patient showed no response.

By December 2023, the median follow-up time was 10.5 months (range, 1.9–26.0 months), and no patient died during the first course of treatment, with 12 (46.2%) patients surviving, five (9.2%) patients having minimal residual disease negative and 14 (53.8%) patients dying. Three, five and six cases of multiple organ failures, primary disease progression and severe infection, respectively were observed. Among them, a patient with multiple organ failure was admitted to the Intensive Care Unit and strongly requested chemotherapy. After full communication and understanding from the family members, chemotherapy was administered according to protocol 1, and bone marrow re-examination indicated partial remission. Subsequently, the patient became unconscious, and treatment was discontinued. The OS and PFS of the patients in two groups were preliminarily analyzed (Fig. 1). The survival analysis of the two groups revealed no significant differences in OS between the two groups (P=0.23; Fig. 1A); however, the PFS rate in the 200 mg group was significantly improved compared with that in the 100 mg group (P=0.037; Fig. 1B). Furthermore, the rate of PFS in the 200 mg group was significantly higher than that in the 100 mg group treated with ≥2 treatment courses (P=0.045), while no significant difference was observed in OS (P=0.34) between the two groups (Fig. 1C and D). By contrast, no significant difference in PFS (P=0.20) and OS (P=0.94) was observed between the two groups after ≥4 treatment courses (Fig. 1E and F).

The most common adverse event during treatment was haematological. All patients had varying degrees of decreased white blood cell counts and neutropenia. In the first course of treatment, the median leukocyte hypoplasia was 1.0×10⁹ cells/l (range, 0.3–17.7×10⁹ cells/l), and the median neutrophil hypoplasia was 0.3×10⁹ cells/l (range, 0.0–13.1×10⁹ cells/l). A total of 15 (57.7%) patients had grade 3/4 febrile agranulocytosis.

All patients had thrombocytopenia, with low PLT values of 20.0×10⁹ cells/l (range, 2.0–231.0×10⁹ cells/l) the first course of treatment; 10 patients had grade 3/4 thrombocytopenia, 13 (>50%) patients did not need PLT infusion during chemotherapy and 11 patients had PLT counts >40×10⁹ cells/l before chemotherapy. Only two patients had PLT counts <40×10⁹ cells/l.

All 26 patients had anaemia, with haemoglobin levels of 55.0 g/l (range, 32.0–99.0 g/l) in the first course of treatment, and 11 (42.3%) patients had grade 3/4 anaemia.

The most common non-haematological adverse reactions were infection and grade 3/4 febrile neutropenia, occurring in eight (30.8%) cases. Pulmonary infection occurred in 22 patients, with 9 (34.6%) patients experiencing grade 3/4 severity. All patients clinically diagnosed with pulmonary fungal infections were treated with drugs such as caspofungin (70 mg first dose, 50 mg subsequent daily dose, for 14 days) and not with strong CYP3A inhibitors such as posaconazole and voriconazole or moderate CYP3A inhibitors such as esaconazole and fluconazole. Gastrointestinal reactions, followed with nausea and vomiting, were observed in three patients (Tables III and IV).

Only one patient (regimen 2) developed tumour lysis syndrome, and none was observed in the 100-mg group.