The patient presents with 1 month hstory of severe spinal pain. There are widspread destructive lesions of the spine. The CBC normal and BM (aspirat, touch) cytology normal.  
BM pathology first report was AML.  
Flow (on only 1% of BM aspirate cells): CD34+, TdT+, CD117-, CD10+, CD22+, CD19+, CD79a+, CD33+, CD13+, cMPO-.  
Molec:  
PML/RARA-, AML1-ETO-, CBFB-MYH1 - //  
bcr/abl, MLL-AF4, TEL-AML1 pending.  
Our diagnosis: B precursor ALL.

B-precursor ALL is very probable since the distribution of CD34, CD79a and Pax5 is similar. Could you show a photo of Tdt and CD10? But - why this discrepancy between flow/smears and biopsy? is there fibrosis (was reticulin stain done?). Could you take a photo of the imprint? there must be some blasts in the smear if there were some cells at all!  
Also, since there is so much of granulopoiesis present it is necessary to exclude CML presenting as lymphatic blasts crisis.

Cavete! AML (M2) with t(8;21) are also PAX5 and sometimes CD19 and CD79a+, please show TdT and CD10 stains since I am not convinced from the pictures here that the blasts are MPO-.  
see also: Tiacci E, Pileri S, Orleth A, et al. PAX5 expression in acute leukemias: higher B-lineage specificity than CD79a and selective association with t(8;21)-acute myelogenous leukemia. Cancer Res 2004;64:7399-404.

My dears, preliminary my idea was AML. Its very diff to access REAL MPO reaction in minor population... After this I get info about FLOW CD79a+ and have found atypical PAX5+ and CD79a+ cells.  
CD10 is in progress.  
Please find some picutres with TdT and some "blastic cells" from touch slide. Appologies for quality- 60x air.

Well, TdT and the smears are quite convincing, AML seems unprobable, I also favor B-LBL

The BM PCR tests are all negative: PML/RARA-, AML1-ETO-, CBFB-MYH1 -, bcr/abl -, MLL-AF4 -, TEL-AML1 -. Cytogenetics pending.

I agree with the previous opinions that this is a B lymphoblastic malignancy. Is the peripheral blood involved? If so, it may be best classified as B-ALL; if not, then B lymphoblastic lymphoma. Where did the figure of 30% come from?

30% "eyballed" estimation from BM impression.

Bone pain as primary presentation of B-ALL is well known. Immunohistochemistry on the biopsy shows blasts CD34,TdT, PAX5 and CD 79a+, well consistent with B-ALL. On flow there is aberrant expression of myeloid markers, CD33 and CD13. I am not sure, but a weak positivity of the blasts for MPO might be present on the last image. Aberrant expression of myeloid antigens in ALL is well documented, however if MPO is really positive a mixed lineage AL should be discussed in the presence of 3 positive myeloid markers. Could you please submit an image 100x magnification of these questionable MPO+ blasts?

Dear Prof. Nina and Collegues, please find additional CD10 and 100x (air, with 100x oil lens) NEW MPO. It seems, that large cells with slight angulated nuclei (blasts?) are MPO +/- at least. In the setting of MPO+++ granulopoesis it's not easy to visualize the real cytoplasmic reaction in relativelly small population of the blasts.  
Thank you for your thoughts. The main lesson of this case: all threpine cases must be immunophenotyped, because these changes can be interpreted as reactive state easilly...I cannot imagine the situation, if these blasts could be CD34- and slipped through the fingers...

BM smears showed some clustering of the blasts but the blast were <5%. BM aspirate was essentialy a dry tap.

Some CYTO 100x oil slides from imprint.

It is difficult, but from the imprints and the other data, I suspect this is CML in blast phase, with separate populations of myeloid and lymphoid lineage blasts, which admittedly, is rare, but has been reported.

Appologies for imprints' and photo quality. We routinelly never deal with aspirates/peripheral blood (clin lab is responsible for it, for blood analyses and for FLOW) and we in our pathology center get sometimes add imprints with BM histology. So really I'm not the professional hematocytologist. The histological picture is not ver specific for myeloproliferation (CML). Without IH the VISUAL IMPRESSION was: some architectural abnormalities with immaturity (mds like or reactive)

bcr/abl negative

Lymphoblasts in the marrow that are CD10, CD34, CD79a, PAX5, TdT positive and CD20 negative: phenotype of precursor B-lymphoblastic leukaemia. I noted BCR/ABL negative which exclude this being blast crisis of CML. In my opinion the MPO 'positivity' of the blasts is background staining.

Thank you all once more for diagnostic support and review.

Dear Ugnius,  
 
Sorry for being late. Do you have an unstained cytology left? You could do cytochemical peroxidase on it and solve the question of MPO positivity. And NSE for monocytes, too.  
Even if MPO is positive in a proven B-line ALL, you have a biphenotype. What is more dangerous - to miss a TdT+ AML, particularly with such a small population seen in flow cytometry: one can easily make a mistake, gating on a wrong subpopulation (a small population or regenerating B-cells, for example). Could you do IgH rearrangement? It would be the final proof of the existance of B clone.  
About monoblasts - they contain a weak dust-like MPO, that could be an explanation of contradictory results. Monocytic markers like CD14, CD11c were not checked (CD33 has no meaning in this setting).  
 
Don't cite me ever, but you have the option of repeated bone marrow if the doubts remain.  

Hematogones have a different immunophenotype from that reported here. Clonality studies are impossible due to a low % of blasts in aspration material. I beleive that CD34+, TdT+, CD117-, CD10+, CD22+, CD19+, CD79a+, CD33+, CD13+, cMPO- immunophenotype is very suggestive of precursor B-ALL.

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