Simple matters in complex times
Authors: Aliyah R. Sohani
Journal: American Journal of Hematology (2017)

The field of hematology/oncology has witnessed a revolution over last few decades in terms of the number and complexity of diagnostic and prognostic tests used in the assessment of hematologic malignancies. In acute myeloid leukemia (AML) alone, diagnosis and prognostication has evolved from relatively simple morphological evaluation (e. g., morphologic blast count, detection of Auer rods, and classical cytogenetics with G-banded karyotype) to more complex testing (e. g., multiparameter flow cytometry, florescence in situ hybridization, and targeted mutational analysis via single gene analysis). More recently, single nucleotide polymorphism array and next generation sequencing, which have the ability to detect point mutations, insertion, and deletions in dozens of genes, are becoming a standard part of assessment at the time of diagnosis. Given these developments, it is remarkable that relatively simple tests requiring visual microscopic evaluation remain highly useful. This principle is illustrated by two studies recently published in the “American Journal of Hematology” highlighting the roles of peripheral blood blast count and bone marrow cellularity in predicting for AML response and outcome. In a study published in a recent issue of the Journal, Short, and colleagues studied the prognostic impact of the rapidity of circulating blast clearance following the initiation of AML induction chemotherapy (day 0) in 363 patients.1 They found that among patients with a WBC count ≥0.4 × 109/L and circulating blasts at diagnosis, those with a day of blast disappearance (DOBD) of ≤5 had a significantly higher complete remission (CR) rate and longer event-free survival (EFS) and overall survival (OS) compared with patients with a DOBD >5. DOBD >5 retained prognostic significance for CR rate, EFS and OS on multivariate analysis, and when patients were stratified by traditional prognostic parameters, including cytogenetic risk group, de novo vs. secondary disease, European Leukemia Net (ELN) risk group, and achievement of CR. In fact, the authors showed that DOBD >5 in the setting of favorable/intermediate cytogenetics or favorable/intermediate-1 ELN risk score was associated with worse OS than DOBD ≤5 in patients who were in the higher risk cytogenetics or ELN subgroups. Although only a minority of patients studied (10%) failed to clear circulating blasts within 5 days, these findings suggest that DOBD >5 represents an enhancement to current risk stratification and may reflect an early marker of chemoresistance. In a second study published in this issue of the Journal, Griffin et al. evaluated various clinicopathologic features at the time of day 14 bone marrow examination in 176 AML patients treated with a second induction chemotherapy regimen (i. e., reinduction) because of residual disease.2 They found day 14 bone marrow core biopsy hypocellularity, using a cut-off of 20% cellularity, to be the strongest predictor of CR achievement following reinduction therapy on univariate and multivariate analysis. Patients who did not achieve CR following reinduction were more likely to have hypercellular day 14 bone marrows. Although the nadir bone marrow cellularity did not retain significance of CR achievement and OS independent of final CR status, the authors’ findings could potentially help guide the need for retreatment, a decision for which evidence-based data are currently limited. For example, by predicting for a lower likelihood of CR achievement, day 14 bone marrow hypercellularity may help to identify patients who could be spared further chemotoxicity and in whom novel treatment approaches should be considered. These studies’ findings and their implications serve to reinforce the importance of judicious morphologic assessment of relatively routine specimens for pathologists and laboratory technologists, as well as the need for individuals involved in obtaining such samples to ensure their adequacy for this assessment. Evaluation of day 14 bone marrow cellularity relies heavily on the bone marrow trephine biopsy, as the aspirate smear does not offer as much information regarding overall cellularity. The World Health Organization recommends that the core biopsy be taken at a right angle to the cortical bone and be at least 1.5 cm in length to enable evaluation of at least 10 partially preserved intertrabecular areas.3 A small specimen or one that is taken parallel to the cortex allows for only subcortical sampling, an area that is often physiologically hypocellular with fewer hematopoietic elements, particularly in older individuals. Assessment of a day 14 bone marrow that is limited by subcortical sampling may therefore lead to a falsely low estimate of overall cellularity or blast percentage if residual disease is present. Absolute blast reduction of >50% was identified by Griffin and colleagues as another factor significantly correlated with CR achievement after reinduction.2 Their findings serve to reinforce to pathologists the importance of evaluation of specimen adequacy, as well as accurate determination of overall cellularity and blast percentage in day 14 bone marrow specimens, as these relatively routine assessments may have a significant impact on clinical outcome. Peripheral blood smears requiring manual review are typically evaluated in the hematology laboratory and are subject to a manual 100-cell or 200-cell count by a laboratory technologist with expertise in the identification and classification of cell types, including blasts. Post-chemotherapy samples pose a number of challenges to laboratories, as such samples are typically leukopenic, making it difficult to identify sufficient numbers of white blood cells for an accurate count, and treatment-induced morphological changes in leukocytes may be present. Laboratories should have criteria in place to ensure that morphologic findings that are unusual or unexpected relative to the patient's clinicopathological context are verified by an experienced technologist or by a pathologist. In addition, the recent advent of digitization of manual smear review and cell counts via automated platforms such as CellaVision (CellaVision AB, Lund, Sweden) provides an opportunity for laboratories to ensure interobserver consistency and potentially to improve sensitivity in the detection of rare cell types. Studies of such technologies have demonstrated very good correlations with traditional 100-cell manual differentials, with superior accuracy depending on cell type and operator experience.4, 5 Automated smear review also provides the opportunity to count a larger number of white blood cells in leukopenic samples, increasing sensitivity and report quality, without severely impacting test result turnaround times.5, 6 Ultimately, both of these recently published studies serve as an important reminder that despite the complex nature of our times, simple things still matter in the diagnostic and clinical practice of hematology.