Case 1: Prerequisites for classification of myeloid neoplasm

Question 1: Which statement is the one best explanation for the discrepancy observed between the blast percentage by bone marrow aspirate visual inspection and the flow-cytometry study?

Correct Answer: C. Flow-cytometry study may not be identifying all of the blasts in the aspirate specimen.

Expert Perspective

Dilution of marrow specimens by peripheral blood, ie, hemodilution, is the explanation for most discrepancies between visual and flow-cytometry blast percentages. However, for the appropriately obtained marrow specimen, flow cytometry may fail to detect all blasts in the specimen if only one blast marker is being employed.  For example, not all leukemic blasts express CD34, particularly monoblasts. If the visual differential includes early promyelocytes in the blast count as recommended by WHO, these cells may express no or little CD34. The addition of at least one additional marker expressed by blasts, such as CD117, CD38, CD123, CD133, or CD200, may aid in a more accurate blast enumeration. 

Although flow cytometry commonly interrogates over 10,000 cells, very little difference will be noted between a 500-cell visual differential and a 500 to 1,500 flow-cytometry analysis by flow cytometry of a nonhemodilute marrow specimen. For acute leukemia and myelodysplasia, neoplastic cell distribution does differ significantly in different areas of the bone marrow.  However, this may not be true for some myeloid neoplasms, including myeloproliferative neoplasms, mastocytosis, and sometimes relapsed acute myeloid leukemia.

Question 2: How can hemodilution of bone marrow aspirates best be avoided?

Correct Answer: B. Perform an aspirate prior to the core biopsy.

Expert Perspective

Hemodilution largely can be diminished by performing the marrow aspirate prior to the core biopsy. The core biopsy may activate the coagulation cascade, resulting in clotting of the subsequent marrow aspirate specimen with low bone marrow particle yield and hemodilution. Performing the aspirate before the core biopsy avoids this problem. Choices C and D, “Collection no less than 0.4 mL of bone marrow aspirate…” and “Reposition the aspirate needle…”  are also good choices and  important to observe. A marrow aspirate collected after the initial 0.5 mL is progressively diluted with sinusoidal blood. Repositioning the biopsy needle after obtainment of 0.5 mL of marrow will ensure a more cellular marrow aspirate specimen.

Question 3: Which of the following statememts is part of the guidelines recommended by WHO (2008) for the evaluation of an initial specimen in patients suspected of having underlying myeloid neoplasms?

Correct Answer: C. At least 500 bone marrow nucleated cells should be counted on a cellular aspirate.

Expert Perspective

The percentage of blasts is important for diagnosis and classification of myeloid neoplasms. In the peripheral blood, the blast percentage should be derived from  a 200 cell leukocyte differential, and in the bone marrow, from the 500-cell count of cellular portions of the BM smear. Not providing detailed clinical information to the hematopathologist will possibly result in his/her performing additional studies that are not necessary, adding to the cost of care, and possibly delaying the diagnosis.

The accurate diagnosis and classification of myeloid neoplasms are often challenging. Thus, a multidisciplinary approach involving a hematologist, hematopathologist, and other specialists (eg, the cytogenetist or molecular pathologist as appropriate) is required to diagnose and classify myeloid neoplasms. Cytogenetic and molecular studies are required at the time of the diagnosis not only for recognition of specific genetically defined entities, but for establishing a baseline against which future studies can be judged to assess disease persistence or progression. Flow-cytometry determination of the blast percentage should not be used as a substitute for visual inspection as already discussed.

Case 2: Optimal bone marrow core biopsy specimen in adults

Question 1: What is an acceptable size of a core biopsy specimen in adults?

Correct Answer: D. At least 1.5 cm

Expert Perspective

The 2008 WHO classification states that the trephine/core specimen “…must be adequate…and at least 1.5 cm in length to enable the evaluation of at least 10 partially preserved inter-trabecular areas.” This guideline is particularly true for the classification of myeloproliferative neoplasms and for marrow evaluation of patients with a suspected diagnosis of myelodysplastic syndrome.

One should not lose sight of the added requirement of “10 relatively preserved inter-trabecular areas,” since even a larger core may have excessive biopsy/crush artifact or excessive aspiration artifact. Other core biopsies, even if 1.5 cm in length, may be suboptimal if they consist of significant amounts of cortical bone and subcortical marrow, the latter of which is normally hypocellular in elderly patients. Excessive amount of cortical bone and subcortical marrow is indicative of the wrong placement angle of the biopsy needle. It should be noted that fixation of core biopsies results in ‘shrinkage’ of 20% to 25%. Thus, the desired biopsy core sample size may have to be at least 2 cm in length.  For young children, biopsies will necessarily be shorter.

In our experience, two biopsies of two different sites provided no more information than obtaining the same amount of core biopsy from a single site. One can argue that the amount of assessable or intact marrow in the biopsy is of more importance than the total length for some hematopoietic neoplasms. For example, as little as 0.5 cm of an intact core biopsy is acceptable in a patient with over 20% myeloblasts in the blood and a suspected diagnosis of acute myeloid leukemia. However, in most adult patients with low blood blast counts, the initial clinical impression is not assured, and one must revert to obtaining the recommended biopsy size.

With the thousands of bone marrow biopsy procedures performed in the U.S. every year, it is striking that little attention has been given to standardization of the procedure and the quality of performed biopsies. A notable exception is a recently published abstract that reports the results of a multi-institutional study of bone marrow core biopsy adequacy and variability in the United States and Canada.² Interestingly, the authors of this study found that “current benchmarks for bone marrow core biopsy adequacy are met in only a minority of cases.” Also noted but not explained was the observation that the “evaluable marrow space” decreased from 2001 to 2011. With the interest in the quality of health care, one should not be surprised if those funding or regulating health care will want assurance that bone marrow biopsies are adequate, informative and performed by individuals with documented competency.  ■

Disclosure: Drs. Abutalib and Behm reported no potential conflicts of interest.

References

1. Swerdlow SH, Campo E, Harris NL, et al: WHO Classification of Tumours of Haematopoietic and Lymphoid Tissuse, 4th ed. Lyon, France, IARC, 2008.

2. Merzianu M, Cheney R, Groman A, et al: Bone marrow core biopsy adequacy and variability in the United Stated and Canada: A multicenter retrospective study. 2014 ASH Annual Meeting and Exposition. Abstract 1316. Presented December 6, 2014.