Is the menin interface a property of the fusion or of the blood? Test KMT2A::MAML2 thymoma
also called menin dependence in thymoma · cross-tissue menin test · KMT2A-MAML2 thymoma revumenib test
The drug that works against KMT2A leukaemias works by breaking the fusion protein's grip on a partner called menin. The same fusion also causes a thymus tumour, so testing whether menin still matters there tells you whether that grip is a property of the fusion itself or of blood cells in particular.
The same thing, for a scientist
A two-stage experiment on KMT2A::MAML2 type B2/B3 thymoma. Stage 1, biochemistry: co-immunoprecipitate menin from fusion-positive thymoma tissue and ask whether the fusion protein is in the complex, alongside fusion-negative thymoma and a KMT2A-rearranged leukaemia line as controls. Stage 2, function: if the interaction is present, treat primary thymoma cells or an established model with a menin inhibitor and read growth, differentiation and the HOXA/MEIS1 programme. The fusion retains MBM1 and MBM2 by position in both tissues - the KMT2A donor exons are 8 to 11, inside the major BCR [E1] - so the graph's standing model predicts the interaction exists. **What makes the experiment worth doing is that either outcome is informative.** Interaction present and inhibitor active: the menin interface is intrinsic to the fusion and an approved drug class has a rationale in a solid tumour with no targeted options [E2]. Interaction absent or inhibitor inactive: menin dependence requires haematopoietic context, which bounds how far the hypothesis generalises. Nothing on this question has been published: the KMT2A/MAML2/menin PubMed intersection is empty [E3].
Stage 1 - does menin bind the fusion in a thymic epithelial cell?1 deeper
Material. Fusion-positive type B2/B3 thymoma, fresh or frozen. This is the hard part: no cell line or public PDX exists, thymomas are resected rather than serially biopsied, and 4% of thymomas carry the fusion 1, so a prospective screen of a thymoma surgical series is needed to find cases. Three to five cases makes the experiment.
Assay. Reciprocal co-immunoprecipitation - menin pull-down blotted for the KMT2A N-terminus, and KMT2A N-terminus pull-down blotted for menin - with proximity-ligation as an orthogonal, single-cell readout that works on fixed tissue and does not need fresh material.
Controls. (i) fusion-negative thymoma, for menin-KMT2A wild-type background; (ii) a KMT2A-rearranged leukaemia line, as the positive control where the interaction is known; (iii) an MBM-deleted construct, if a model is ever built.
Why start here rather than with the drug. A growth experiment with a menin inhibitor conflates the fusion-menin interaction with menin's own functions in thymic epithelium, which are not characterised. The biochemistry is unambiguous and the pharmacology is not.
What a negative Stage 1 would mean
If menin does not co-precipitate with the fusion in thymoma but does in the leukaemia control, the interface is context-dependent. The immediate follow-up is to ask what supplies the context: LEDGF/PSIP1 expression, the chromatin state of the HOXA cluster, or the presence of a partner-specific complex. That is a more interesting result than the positive one, and it would put a boundary on a hypothesis this project treats as close to general.
Stage 2 - does a menin inhibitor do anything?
Run only if Stage 1 is positive.
Readouts, in order of interpretability.
- HOXA9 and MEIS1 transcript levels before and after treatment. This is the proximal pharmacodynamic marker and it is interpretable even if growth does not change. It also answers a separate open question: whether the canonical KMT2A-r transcriptional programme runs at all in an epithelial cell.
- Fusion-protein occupancy at HOXA by CUT&RUN, before and after.
- Growth and viability in primary culture or explant.
- Differentiation markers, since the disease is an epithelial neoplasm and the leukaemia readout (differentiation block release) does not transfer.
Comparator. Revumenib is the approved agent and would be the obvious choice; a structurally unrelated menin inhibitor as a second arm guards against compound-specific effects 2.
Why this beats the alternatives
The other ways to ask whether the menin interface is intrinsic all require building something first: a KMT2A::MAML2 leukaemia model that does not exist, a knock-in mouse, or a comparison across fusion partners that confounds partner identity with everything else. The thymoma cases already exist in human tissue archives. They hold the oncogene constant, vary only the cell, and were produced by nature rather than by a construct. That is a cleaner comparison than anything a laboratory can build, and its cost is a tissue-access problem rather than a biology problem.
A collaboration with a thymic-tumour pathology group is the rate-limiting step, not an assay.
| design | Stage 1: reciprocal co-immunoprecipitation of menin and the KMT2A N-terminus from 3-5 fusion-positive type B2/B3 thymomas, with proximity-ligation as an orthogonal fixed-tissue readout. Controls: fusion-negative thymoma, a KMT2A-rearranged leukaemia line as positive control. Stage 2 (only if Stage 1 is positive): menin-inhibitor treatment of primary thymoma cells or explants, two structurally unrelated inhibitors. |
|---|---|
| readout | Stage 1: presence of the fusion protein in the menin complex and vice versa. Stage 2, in order of interpretability: HOXA9/MEIS1 transcript change; fusion occupancy at HOXA by CUT&RUN; growth and viability; epithelial differentiation markers. |
| controls | fusion-negative thymoma (wild-type menin-KMT2A background); KMT2A-rearranged leukaemia line (known-positive interaction); second structurally unrelated menin inhibitor in Stage 2 to exclude compound-specific effects. |
| cost tier | med |
| timeline | Dominated by tissue access, not assay time. 12-18 months assuming a prospective collaboration with a thymic-tumour pathology group; the bench work is 3-4 months once material is in hand. |
| rate limiting step | Finding fusion-positive thymoma tissue. No cell line or public PDX exists, thymomas are resected once rather than biopsied serially, and only 4% carry the fusion. |
| decision rule | Menin co-precipitates with the fusion in thymoma -> the menin interface is intrinsic to the fusion protein and generalises beyond haematopoiesis. It does not -> menin dependence requires haematopoietic context, and the next question is what supplies that context. |
| what it does not test | Whether menin inhibition is clinically useful in thymoma (a growth readout in explants is not an efficacy signal); whether MAML2 contributes anything; whether the Notch dominant-negative effect operates in epithelium. |
bears on
[ "hyp-menin-primacy-is-geometry-not-biology", "hyp-menin-inhibition-is-tissue-divergent", "disease-kmt2a-maml2-thymoma", "fusion-kmt2a-maml2" ]
- A positive result invites long-duration menin-inhibitor dosing in middle-aged adults with a tumour that is often not immediately life-threatening. This graph already holds entries on the class's endocrine and multi-organ hyperplasia signal and on exposure duration versus MEN1 latency; the risk arithmetic in a chronic epithelial tumour is not the arithmetic of relapsed acute leukaemia and should not be imported from it.
- A negative Stage 2 result with a positive Stage 1 is the worst outcome to interpret: the interaction exists but the drug does nothing, which could mean epithelial cells do not depend on the HOXA programme, or that the explant assay is inadequate, or that menin's own epithelial functions mask the effect. Pre-register which of those would be pursued.
- Running this experiment means asking a surgical pathology service to divert scarce tumour tissue from diagnosis to research in a rare tumour. That is a real cost borne by patients who will not benefit from the result.
- Which thymic-tumour pathology groups hold fusion-annotated material? The 2020 series was assembled between Massachusetts General Hospital and a commercial profiling laboratory, so the tissue and the annotation are in known hands and the collaboration is identifiable rather than hypothetical.
- Can proximity ligation on archival FFPE thymoma substitute for co-immunoprecipitation on fresh tissue? If so the experiment becomes a retrospective study on existing blocks and the timeline collapses from 18 months to about 4.
- Should the same design be run on KMT2A::USP2 leukaemia in parallel? That fusion also has untested menin dependence and is the other half of this beat's menin gap - but it has no model either, so it faces the same material problem without the archival-tissue advantage.
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
KMT2A-MAML2 thymomas break at KMT2A exon 8, 9, 10 or 11 - inside the major BCR and 5' of everything it removes - so the fusion protein retains the menin-binding motifs by position, in 11 patients at 4% of all thymomas and 6% of B2/B3 histology.
Pan-Cancer Landscape Analysis Reveals Recurrent KMT2A-MAML2 Gene Fusion in Aggressive Histologic Subtypes of Thymoma. · Massoth LR, Hung YP, Dias-Santagata D, Onozato M, Shah N, Severson E, Duncan D, Gillespie BJ, Williams NF, Ross JS, Vergilio JA, Harkins SK, Glomski K, Nardi V, Zukerberg LR, Hasserjian RP, Louissaint A, Williams EA · JCO Precision Oncology 2020What this evidence cannot show
Retention of the menin-binding motifs is inferred from breakpoint position and the KMT2A domain map, not demonstrated at the protein level in any thymoma. The cohort is a commercial advanced-cancer profiling series, so the 4% frequency may overstate what a general thymoma surgical series would yield, which matters directly for how many cases a prospective screen would need. Abstract read in full.
Evidence that argues against this (1)
- Positional retention of a motif is not the same as a functional interface. The fusion protein has never been purified from any tissue, and a thymic epithelial cell may post-translationally modify or occlude the N-terminus in ways a leukaemic blast does not. This is precisely why the proposed experiment starts with biochemistry rather than pharmacology. Nemoto N et al. 2007
- E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Thymomas harbour a relatively low mutational burden and lack genetic alterations usable prognostically or therapeutically, which is why the authors present KMT2A-MAML2 as potentially clinically relevant for patients with disease refractory to conventional therapy.
Pan-Cancer Landscape Analysis Reveals Recurrent KMT2A-MAML2 Gene Fusion in Aggressive Histologic Subtypes of Thymoma. · Massoth LR, Hung YP, Dias-Santagata D, Onozato M, Shah N, Severson E, Duncan D, Gillespie BJ, Williams NF, Ross JS, Vergilio JA, Harkins SK, Glomski K, Nardi V, Zukerberg LR, Hasserjian RP, Louissaint A, Williams EA · JCO Precision Oncology 2020What this evidence cannot show
The clinical-relevance statement is the authors' framing of an opportunity, not a demonstration that any drug works. No treatment of a fusion-positive thymoma with any targeted agent has been reported. 'Low mutational burden' is a cohort-level statement about thymoma and is not specific to the fusion-positive subset. Abstract read in full.
Evidence that argues against this (1)
- Type B2/B3 thymoma is often managed successfully by surgery and radiotherapy, so the population that would actually need a targeted agent is the refractory or metastatic minority of a 4% subset of an uncommon tumour. The clinical opportunity is real but numerically small, and that affects whether any sponsor would pursue it. Zhou Z et al. 2025
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.database
Nothing has been published on menin in the context of KMT2A-MAML2 in any tissue: the PubMed intersection (MLL OR KMT2A) AND MAML2 AND menin returns zero records.
PubMed E-utilities esearch counts for KMT2A/MAML2/menin intersection queries, run 2026-09-19 · National Center for Biotechnology Information (NCBI), PubMed · PubMed (NCBI E-utilities) 2026What this evidence cannot show
A counted-absence claim, only as good as the symbol set; run over MAML2, MEN1 and menin, not over every menin-inhibitor name, and it would miss any paper not naming both genes in an indexed field. A snapshot of one day's index.
Evidence that argues against this (1)
- Menin dependence is treated in the field as a general property of major-BCR KMT2A fusions, so a group that tested it and found the expected answer might never publish it as a MAML2-specific result. The empty intersection reflects what is indexed, not necessarily what is known. Massoth LR et al. 2020
co-IP of menin with the fusion from thymoma tissue, then menin-inhibitor response - never done, zero PubMed records
asks whether the menin interface is intrinsic to the fusion protein or requires haematopoietic context
a cross-tissue test of whether menin primacy travels with the fusion or with the cell
thymic epithelium is a tissue in which menin-inhibitor effect has never been examined