Nobody has ever stratified any KMT2A::MLLT1 outcome or drug-response analysis by reciprocal or spliced status - a measured absence, with the queries

All counts were taken with retmode=json and the querytranslation field inspected.

A quoted phrase that PubMed does not hold in its phrase index is silently abandoned and re-mapped to a MeSH-expanded OR query. Measured here:

"spliced fusion"  AND leukemia  -> count 0
    qt: "spliced fusion"[All Fields] AND (...)          phrase honoured
"spliced fusions" AND leukemia  -> count 567
    qt: ("rna splicing"[MeSH Terms] OR ("rna"[All Fields] AND
         "splicing"[All Fields]) OR ... OR "spliced"[All Fields] ...)
                                                        phrase ABANDONED

The singular is a real bounded zero. The plural is not a 567-fold richer literature; it is a different query that PubMed wrote. The brief already warns that singular and plural are different [tiab] queries; this is the sharper version - quoting does not guarantee phrase matching, and the failure is visible only in querytranslation. A beat that ran the plural and reported '567 records on spliced fusions in leukaemia' would be reporting on RNA splicing in general.

In 90 paediatric MLL-rearranged acute leukaemia patients, 37.8% (34/90) had a single direct MLL fusion gene, 15.6% (14/90) a single reciprocal fusion and 27.8% (25/90) both reciprocal alleles; children with reciprocal MLL fusions had relatively favourable outcomes against children with complex translocations or a single direct allele, 66.1% versus 24.6% and 27.6%, P = 0.001 1. This is, as far as these searches reach, the only clinical outcome analysis in the literature stratified by reciprocal-fusion status. It pools every partner gene, so partner identity and reciprocal status are confounded - and partner identity is itself prognostic and lineage-dependent in this disease. It is chemotherapy-era, n = 77 treated, median follow-up 2.5 years, no MLLT1 breakout and no drug-response endpoint. Its direction (reciprocal-positive does better) matches the t(4;11) infant finding, which makes the pooled result consistent with an AFF1-driven signal rather than a general one.

• PMID 12781363 and PMID 17906700, the Rabbitts/Forster Cre-loxP Mll-Enl translocator mice. On-topic by title - these are literally reciprocal chromosomal translocations - but they are model-construction papers: neither compares reciprocal-positive with reciprocal-negative animals, because every animal is reciprocal-positive by design. Recorded separately in concept-mouse-mll-enl-models-are-reciprocal-positive-by-construction.
• PMID 32766858, 'Exploitable metabolic dependencies in MLL-ENL-induced leukemia'. Surfaces in two of the searches above and is a genuine MLL-ENL paper; it is a metabolic-dependency study with no reciprocal or breakpoint stratification.
• PMID 34489550 and PMID 34354240, the Marschalek 'role of reciprocal fusions in MLL-r acute leukemia' series. A search on the series title returns count 2: the t(4;11) and t(6;11) instalments. There is no t(11;19) instalment, and MLLT1 is the partner with by far the largest reciprocal-negative class.
• PMID 29384595 and PMID 32991719, partner-stratified AML outcome papers. Both stratify by partner and neither measures reciprocal status; they are cited elsewhere in this graph for the partner question.

What would change the conclusion: any paper reporting outcome, HOXA signature, MRD kinetics or drug response separately for MLLT1 patients with and without a reciprocal allele; or a supplementary table in a recombinome-derived paper that crosses breakpoint class with any endpoint.