Incidence and Outcomes of T-Cell Acute Lymphoblastic Leukemia (T-ALL) in United States

Background:

T-ALL is a highly curable malignancy in the pediatric population. In adults, numerous treatment options are available in the current era, both in newly diagnosed and relapsed setting. However, population-level data on the incidence and outcomes of T-ALL in United States is sparse.

Methods:

Using Surveillance Epidemiology and End Results (SEER-18) database, we retrospectively identified patients aged ≥ 20 years with pathologically confirmed T-ALL (ICD-0-3 codes 9729, 9837) as the first primary malignancy, known race, diagnosed between the years 2001-2014 and actively followed. We aimed to determine the trends in incidence and overall survival (OS) of T-ALL in United States. Incidence rate per 100000 population and incidence rate ratio (IRR) were calculated to describe the relative differences in disease incidence between subgroups. OS was calculated by Kaplan-Meier method and compared by log rank test with determinants analyzed by Cox-proportional hazard regression method. For survival analysis, only patients treated with chemotherapy were included. Statistical analyses were done with a two sided significance level of p < 0.05.

Results:

We identified 1035 patients with T-ALL who met the study criteria. Median age of the cohort was 35 years (range 20-100 years). Majority of the patients were in the age group 20-39 years (58.8%), males (67.8%) and White race (75.1%). Overall incidence of T-ALL was 0.13 cases per 100000 population. Incidence decreased significantly after the age 40 (IRR ranging from 0.51 to 0.55, p <0.01) and increased from the year 2003 onwards (IRR ranging from 1.66 to 2.66, p <0.01) (Table 1). Compared to White race, Blacks (IRR 1.28, p < 0.01) had higher disease incidence. Females had a lower disease incidence than males (IRR 0.47, p<0.01). The 5-year OS declined significantly with increasing age (age <40 - 52.8%, age 40-59- 37.6%, age 60-79- 21.7%, age ≥ 80- 0%, p<0.01). The 5-year OS did not significantly vary by gender (males- 44.6% vs. females- 43.8%, p = 0.83), but varied by race (Whites- 48.1%, Blacks- 25.4%, others- 44%, p<0.01). Over time, the 5-year OS has improved significantly (year 2001-2007- 40.1% vs. 2008-2014 - 48.7%, p=0.01) (Figure 1). On multivariate analysis, increasing age (age 40-59- HR 1.61, 95% CI 1.32-1.96; age 60-79- HR 2.51, 95% CI 1.94-3.25; age ≥80- HR 5.01, 95% CI 2.78-9.01, p<0.01) and Black race (HR 1.74, 95%CI 1.39-2.19, p<0.01) were associated with significantly higher risk of mortality. Diagnosis in the period 2008-2014 was associated with a significantly lower mortality (HR 0.78, 95% CI 0.65-0.93, p <0.01).

Conclusions:

The incidence of T-ALL varies by age, gender, race and period of diagnosis. OS decreases with increasing age and is inferior in Black race. Over time, the survival of T-ALL has significantly improved likely due to the practice of using pediatric inspired chemotherapy, salvage treatment options, better supportive care and stem cell transplantation.

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