Acute Promyelocytic Leukaemia Presenting as Myeloid Sarcoma
Bibliographic record
Abstract
Background: Myeloid sarcoma (MS) is a rare entity most often found concurrently with acute myeloid leukemia (AML) but may rarely precede blood or bone marrow involvement thus presenting a diagnostic challenge. The World Health Organization considers MS synonymous with AML, and recommends the tumor be classified into an AML subgroup. Acute promyelocytic leukemia (APL) presenting as MS is exceedingly rare. Methods: We report the case of a 19-yr-old female patient presenting with severe back pain, weight loss, epistaxis, and falling fibrinogen levels suggestive of disseminated intravascular coagulation. Bone scan revealed multiple vertebral compression fractures; positron emission tomography-computed tomography showed extensive, variably hypermetabolic, disseminated skeletal lesions. Needle core biopsy of an L6 vertebral mass revealed a dense population of monomorphic cells with uniform round to ovoid nuclei, variably granular to vacuolated pale-staining cytoplasm, areas of necrosis, and scattered mitotic figures. Immunohistochemical (IHC) studies showed diffuse membranous CD99 positivity with no apparent expression of CD45, CD43, CD56, TdT, CD20, CD79a, CD34, CD138, AE1/AE3, desmin, or synaptophysin, leading to an initial suspicion of Ewing sarcoma. However, the finding of strong myeloperoxidase staining led to additional IHC studies, which demonstrated positive lysozyme, CD68, and weak CD117 expression. Subsequent testing with nested polymerase chain reaction identified PML-RARA; the diagnosis of APL was conferred. Conclusions: This case is an extremely rare presentation of APL. The diagnosis of MS can be challenging and may be missed without a high level of clinical suspicion and a comprehensive IHC panel. APL can be particularly challenging, as it is often apparently negative for common hematologic markers, including CD34, which would typically be positive in AML. Myeloperoxidase is a specific marker of myeloid lineage and highly sensitive for acute promyelocytic leukemia. The inclusion of myeloperoxidase in the IHC panel for a poorly differentiated malignancy is a reliable way of excluding acute promyelocytic leukemia.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".