CNS involvement at diagnosis and its association with CNS toxicities in childhood ALL

Central nervous system (CNS) leukemia is clinically characterized by the presence of leukemic cells in cerebrospinal fluid (CSF). Routine diagnosis by cytomorphology (CM) has been linked to an increased risk of CNS toxicities and early posterior reversible encephalopathy syndrome (PRES) in recent studies. Flow cytometric immunophenotyping (FCI), which is a less commonly used diagnostic tool, can detect low levels of leukemic blasts in the CSF and has a higher sensitivity than CM.

CNS-directed chemotherapy is administered to all patients with acute lymphoblastic leukemia (ALL) at diagnosis as a preventative measure against CNS relapse, regardless of CNS involvement. On the other hand, enhanced intrathecal chemotherapy, which has been associated with CNS toxicities, is given to patients with ALL on diagnosis of CNS leukemia. There is still uncertainty as to whether CNS toxicities are due to directed CNS prophylactic measures, or a result of the presence of leukemic cells in the CNS.

Here, we summarize a recently published article by Anastasopoulou et al.¹ in Blood, investigating the role of minimal CNS involvement at diagnosis on the risk of CNS toxicities by FCI in pediatric patients with ALL.

Methods

Patients included in the analysis were

• children aged 1–17.9 years;
• diagnosed with ALL between 2008 and 2015;
• treated according to the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL2008 protocol; and
• had diagnostic data on CNS involvement by both CSF by FCI and CM.

CNS involvement by CM categorized patients into three groups:

• CNS1: no CNS involvement
• CNS2: <5 /μl leukemic cells and blasts in the CSF
• CNS3: ≥5 /μl leukemic cells and blasts in the CSF or clinical signs of CNS involvement

CNS involvement by FCI classified patients into two groups:

• positive for CNS involvement (CNS_flow+): ≥10 leukemic blasts in the CSF by FCI
• negative for CNS involvement (CNS_flow−): <10 leukemic blasts in the CSF by FCI

The three groups of CNS toxicities in patients were:

• all CNS toxicities (including any associated toxicity)
• seizures (both isolated and secondary to CNS toxicities)
• PRES

The study endpoints were the association between CNS leukemia by FCI at diagnosis and the risk of CNS toxicities; the association of CNS_flow+ with CNS toxicity was also tested.

Results

Baseline clinical characteristics and toxicities

Overall, 370 patients were included in the study. Within the CNS1 group (n = 320), 256 were CNS_flow− and 64 were CNS_flow+, as seen in Figure 1.

Figure 1. Patient classification of CNS involvement at diagnosis based on combined CM and CSF FCI data* 

ALL, acute lymphoblastic leukemia; CM, cytomorphology; CNS, central nervous system; FCI, flow cytometric immunophenotyping; NOPHO, Nordic Society of Paediatric Haematology and Oncology.
*Data from Anastasopoulou, et al.¹

At baseline, 38 patients overall reported at least one type of CNS toxicity, with 22 of these cases occurring with seizures. Of these 22, 16 cases were associated with PRES. In CNS1 patients who were CNS_flow+, there was a total of 33 CNS toxicity cases; 18 presented with seizures and 14 of these related to PRES.

Clinical characteristics that were significantly higher at diagnosis in CNS1 patients with CNS_flow+ included white blood cell count and T-cell immunophenotypes (p < 0.001; Table 1).

Table 1. Clinical characteristics at diagnosis of CNS1 patients*

The univariate analysis in all CNS_flow+ patients, which included both patients who received (CNS1) and did not receive enhanced intrathecal treatment (CNS2 and CNS3), revealed an increased risk for seizures (hazard ratio [HR], 2.72; 95% confidence interval [CI], 1.18–6.28; p = 0.019] and PRES (HR, 2.72; 95% CI, 1.18–6.28; p = 0.019) when compared with CNS_flow− patients. After adjusting for the type of induction therapy in the multivariate analysis, patients with CNS_flow+ still had a significant risk for PRES (HR, 2.72; 95% CI, 1.18-6.28; p = 0.019).

Among CNS1 patients who did not receive enhanced intrathecal treatment, univariate analysis showed that CNS_flow+ status alone was associated with an increased risk of all CNS toxicities, seizures, and PRES when compared with toxicities in CNS_flow- patients . In the multivariate analyses, which adjusted for age and subsequently induction therapy, CNS1_flow+ status was still a significant risk factor for all CNS toxicities (Table 2).

Table 2. Risk of CNS toxicity in CNS1 patients*

Conclusion

This study demonstrated that minimal CNS involvement without enhanced CNS chemotherapy, as determined by FCI, is significantly associated with an increased risk for CNS toxicities, with the highest risk seen for PRES. Despite the small cohort, both univariate and multivariate analyses reported a positive association between CNS leukemia and risk of CNS toxicities. These results can be a foundation for future studies on the allocation of CNS prophylactic measures.