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Under pressure from a drug that blocks its identity (the androgen receptor in prostate cancer, EGFR in lung cancer), a tumour can change what kind of cell it is, becoming a small-cell neuroendocrine cancer that no longer needs the blocked signal. It is the ultimate escape: not a new mutation in the engine, but a new engine.
Lineage plasticity requires loss of the gatekeepers TP53 and RB1 (Ku et al., Mu et al. 2017), which unlocks SOX2, EZH2-mediated repression of lineage genes, and reactivation of neural programmes (ASCL1, NEUROD1, INSM1, BRN2), producing AR-indifferent neuroendocrine prostate cancer in 15-20% of castration-resistant cases after potent AR inhibitors, and small-cell transformation in ~5-15% of EGFR-mutant NSCLC on osimertinib (also after ALK inhibitors and in immunotherapy-treated adenocarcinoma). Related transitions: squamous transdifferentiation of adenocarcinoma, sarcomatoid dedifferentiation in RCC and mesothelioma, MITF-low neural-crest states in melanoma under BRAF inhibitors, and blast/Richter transformation in lymphoid cancers. The new state expresses DLL3, SEZ6, B7-H3, CEACAM5 and loses PSMA or EGFR dependence, is transiently sensitive to platinum-etoposide, and is detected by biopsy at progression (recommended when PSA is low relative to disease burden or ctDNA shows TP53/RB1 loss) and by DLL3 PET. Therapeutics: DLL3 engagers (tarlatamab), EZH2 inhibitors (mevrometostat + enzalutamide, tazemetostat) to block or reverse the switch, Aurora A inhibitors for MYCN/ASCL1 states, and B7-H3 or SEZ6 ADCs.
A shop that sells hats is fined every time it sells a hat (AR blockade). One day it reopens as a bakery. The fine no longer applies, the old inspectors (PSA, PSMA scans) see nothing, and only a new set of tools works against the new business.
It is the right shape of answer for a transition that is epigenetic rather than genetic, and it could in principle spare the biopsy that is currently the only way to make this diagnosis.
It offers the first credible explanation for why only a minority of small-cell patients get a durable benefit from checkpoint blockade, and it introduces subtype switching, which would mean retesting at relapse rather than typing once.
It is the reality check on the subtype model and it has a direct consequence for treatment: the DLL3-directed medicines are aimed at the neuroendocrine-high subtypes, and the POU2F3 and double-negative tumours will not express the target.
It gives the sequencing report a prognostic reading that does not depend on a repeat biopsy: an EGFR-mutant cancer that also carries RB1 and TP53 alterations will stop responding sooner and should be watched for a change of histology.
It is the practical guide to what to do after transformation: treat it as small-cell lung cancer with platinum and etoposide, expect central nervous system disease, and do not expect a checkpoint inhibitor to help.
It is the most disciplined outcome analysis in this disease and its result is deflationary in a useful way: most of the alterations people quote as prognostic do not survive adjustment, and the one that does, RB1, is also the one that marks the route to neuroendocrine transformation.
It gives the field a vocabulary for the states between androgen receptor-driven adenocarcinoma and small cell carcinoma, which matters because those in-between tumours are the ones most likely to be mismanaged as ordinary castration-resistant disease.
The organising framework for every small-cell lung cancer trial designed since. It is also why the slow progress in the disease is now attributed to treating four diseases as one rather than to the biology being intractable.
Shares ASCL1, SOX2, Molecular profiling stratifies diverse phenotypes of treatment-refractory metastatic castration-resistant prostate cancer, Patterns of transcription factor programs and immune pathway activation define four major subtypes of SCLC with distinct therapeutic vulnerabilities and the tags mechanism, mechanics-atlas.
Shares Cancer stem cell theory and phenotypic plasticity, Cancer stem cells & phenotypic plasticity, EZH2, Resistance routes: how a blocked pathway comes back and the tags mechanism, mechanics-atlas.
Shares Small cell lung cancer (KEGG map), Non-small cell lung cancer (KEGG map), p53 / RB / cell-cycle checkpoint, TP53 and the tags mechanism, mechanics-atlas.
Shares Cancer stem cells & phenotypic plasticity, Resistance routes: how a blocked pathway comes back, Acquired resistance to every therapy, Antibody-drug conjugate (ADC) and the tags mechanism, mechanics-atlas.
Shares Analysis of tumor specimens at the time of acquired resistance to EGFR-TKI therapy in 155 patients with EGFR-mutant lung cancers, Prostate cancer (KEGG map), Non-small cell lung cancer (KEGG map), Resistance routes: how a blocked pathway comes back and the tags mechanism, mechanics-atlas.
Shares Molecular characterisation of neuroendocrine prostate cancer and identification of new drug targets, p53 / RB / cell-cycle checkpoint, TP53, Antibody-drug conjugate (ADC) and the tags mechanism, mechanics-atlas.
Shares Osimertinib, EGFR, Small-cell lung cancer, Melanoma and the tags mechanism, mechanics-atlas.
Shares Tazemetostat, EZH2, Epigenetic drugs (HDAC, DNMT, EZH2, IDH, menin, BET), T-cell engagers (bispecific) and the tags mechanism, mechanics-atlas.