myeloid sarcoma designation question

[cellmatrix]

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I recently encountered a case of a 10 cm rectal tumor in a patient with a history of CMML-2 diagnosed 1 month prior on bone marrow biopsy. Morphologically, the malignant cellular infiltrate effaced the submucosa and subserosa, with focal involvement of the colonic epithelium. The tumor cells were heterogeneous, and only some showed nuclear folding. Many even showed plasmacytic features, others demonstrated an appearance similar to large transformed lymphocytes. Only occasional cells had a primitive blast like appearance. No immunstains for either MPO, CD68, lysozyme, or CD123 were done. The diagnosis was simply rendered "Granulocytic Sarcoma" on the basis of morphology and history. Obviously in a patient with a prior diagnosis of a leukemic process (in this case, CMML-2 with 15% myeloid blasts in the marrow), any high grade extramedullary hematopoietic infiltrate is myeloid sarcoma until proven otherwise, especially when forming a large mass. But without immunostains to demonstrate tumor composition predominantly by myeloid blasts representing expansion of the CMML-2 myeloid blast subset (and hence evolution to an AML with extramedullary tissue involvement), how can you be sure that the tumor mass was not simply, "extramedullary tissue involvement by CMML-2". I doubt that tissue infiltration by CMML-2 would form a large, discrete tumor mass, however morphologically the cellular infiltrate did not have the appearance of predominant composition by myeloid blasts. I think had a hematopathologist signed out the case the standard of care would have called for performance of immunostains. I'll likely pull the block from the warehouse and just do immunostains and see, but I'm curious about what others may think. Thanks!

 

[Gene_]

A destructive soft tissue lesion composed of myeloid cells is myeloid sarcoma. You don't need sheets of blasts or even a predominance of blasts to call it. The destructive nature of the lesion is the most helpful feature. Immunostains are not very helpful. I would have ordered an MPO though, just to be absolutely sure of what I was dealing with. If they looked like transformed lymphs like you say, I'd toss a CD3 and CD20 at it too.

 

[pathstudent]

I once saw a skin lesion with a cmml infiltrate in a cmml person that was called myeloid sarcoma by a well respected academic dermpath. It was reviewed by the myeloid god vardiman and he said while it was certainly a "leukemia cutis", it should not be called myeloid sarcoma without being blasts. Myeloid sarcoma would imply transformation to aml.

 

[caffeinegirl]

Hmmm...I haven't looked this up in a while but my understanding is that a mass/nodule composed of blasts is a myeloid sarcoma (which can precede full blown leukemia) and that a cutaneous infiltrate in a patient with leukemia (which does not form a mass/nodule but usually appears as papules or erythematous plaques) is leukemia cutis, which confers a poor prognosis. In the rectal tumor, it would be a myeloid/granolocytic sarcoma. However, if you had a rectal biopsy of a "bump/minute polyp/erythema" and you had an inflammatory infiltrate (not mass-forming) composed of atypical/neoplastic cells with the immunophenotype of the circulating leukemia cells, then it's "involvement by X type of leukemia).
The distinction is important. For example, let's say a patient had a h/o of AML now in remission and presents with a mass with no apparent circulating blasts in the peripheral blood. The mass turns out to be sheets of blasts...then it's myeloid sarcoma. Doesn't mean the patient has an AML relapse...yet.

 

[Ruination]

Agree with caffeinegirl.

From the WHO:
"Tumor mass c/o myeloid blasts with or without maturation occuring at an anatomical site other than the bone marrow. Infiltrates of any site of the body by myeloid blasts in leukemic patients are NOT classified as myeloid sarcoma unless they present with tumor masses in which the tissue architecture is effaced."

Clinically, its considered as an equivalent diagnosis to AML. I'd throw some stains on it (CD68, lysozyme and whatever might have been + previously and is available in paraffin) and then see if there are >20% blasts in the marrow or peripheral blood. This likely represents disease progression from this patient's MDS/MPN.

 

[cellmatrix]

The situation boils down to differential diagnosis between myeloid sarcoma and tissue infiltration by chronic myelomonocytic leukemia 2. I think most would agree that myeloid sarcoma is a tumor predominantly composed of myeloid blasts. Rendering diagnosis of myeloid sarcoma in a cmml2 patient implies evolution to acute leukemia. This is analogous to a cml accelerated phase patient developing granulocytic sarcoma...in such a situation the patient is then essentially in blast crisis phase. I think it is important to demonstrate predominant composition of the rectal tumor by blasts in this instance, and I think the logic parallels that of the leukemia cutis case referenced in the above post. I think the lesion is granulocytic sarcoma until proven otherwise, but it is incumbent to demonstrate predominant composition greater than 20 percent by myeloid blasts.

 

[Gene_]

For example, let's say a patient had a h/o of AML now in remission and presents with a mass with no apparent circulating blasts in the peripheral blood. The mass turns out to be sheets of blasts...then it's myeloid sarcoma. Doesn't mean the patient has an AML relapse...yet.

Actually, that is defined as a relapse.

A source of confusion in preceding posts is the perceived requirement for a certain percentage of blasts. Blasts are present, yes. But, there is no requirement for >20% blasts, a predominance of blasts or sheets of blasts. Those things are common if you're are dealing with AML. But, think about myeloid sarcoma arising in CML or CMML. These are both clonal processes that have myeloid maturation. It should not be too surprising that a myeloid sarcoma arising in either of these entities may have significant component of maturation and relatively few blasts.

 

[Ruination]

Actually, that is defined as a relapse.

A source of confusion in preceding posts is the perceived requirement for a certain percentage of blasts. Blasts are present, yes. But, there is no requirement for >20% blasts, a predominance of blasts or sheets of blasts. Those things are common if you're are dealing with AML. But, think about myeloid sarcoma arising in CML or CMML. These are both clonal processes that have myeloid maturation. It should not be too surprising that a myeloid sarcoma arising in either of these entities may have significant component of maturation and relatively few blasts.

Extramedullary blast population in CML is by definition "CML in blast crisis" which most oncologists treat with AML therapy+ TKIs. The CML in blast crisis that I have seen have shown progression as typical myeloid or lymphoid blasts; I haven't seen a case with monocytic differentiation. My point was that the peripheral blood and bone marrow need to be evaluated for blasts or blast equivalents (promonocytes or monoblasts) in the evaluation of this patient. This person may meet criteria for a diagnosis of AML based on the medullary component of her disease, thus rendering this conversation moot.

 

[malchik]

This thread should be closed immediately. We only discuss the job market here.

 

[caffeinegirl]

Actually, that is defined as a relapse.

doh! Well that shows my weakness in hemepath I guess...I'm just going by my "understanding" which didn't involve actually looking into the books...was hoping somebody would correct me. Usually if there is a diagnosis of granulocytic/myeloid sarcoma the heme onc's know to check out the peripheral blood and marrow for involvement as well.

 

[pathstudent]

The important thng is that a cmml infiltrate, mass forming or not, should never be diagnosed as a myeloid sarcoma unless it satisfies the requirement for aml.

But let's face it and stop beating the bush, if you have a cmml and have a tissue forming mass of cmml or aml, you are pretty much hosed either way.

 

[Ruination]

This thread should be closed immediately. We only discuss the job market here.

👍 So true. I love discussing cases. Its too bad that's not what happens here for the most part.