The significance of the finding lies in the sheer scale of the problem it addresses. Roughly a quarter of all lung adenocarcinomas carry mutations in the KRAS gene, a well-known oncogene that drives uncontrolled cell proliferation by locking cellular growth circuits into the on position. After decades in which KRAS was considered undruggable, the United States Food and Drug Administration has in recent years approved two inhibitors that specifically target a common mutation known as KRAS-G12C. These drugs represented a genuine milestone for patients whose tumors had stopped responding to other treatments, and they can produce meaningful initial responses. Yet the clinical experience has been sobering: while the inhibitors work in about 35 percent of the patients who receive them, tumors almost invariably develop resistance, and most cases eventually relapse.

Until now, the dominant explanation for that resistance has been genetic. Tumor cells typically reactivate KRAS signaling through secondary mutations that prevent the drug from binding to its target, or by producing additional copies of the KRAS gene so that the sheer abundance of the protein overwhelms the inhibitor. Both routes converge on the same destination: sustained activity of the MAP kinase signaling pathway, the growth-promoting cascade that KRAS normally triggers and that fuels cell division. A 2021 study from researchers at Dana-Farber Cancer Institute, which analyzed tumors from 17 patients with non-small cell lung cancer treated with KRAS-G12C inhibition, identified such secondary resistance mutations in a majority of the patients examined. But that study also contained a puzzle. In two of the patients, the tumors showed no obvious resistance mutations at all. Instead, they had transformed from adenocarcinomas into squamous cell carcinomas, a completely different class of lung tumor.

That observation is more remarkable than it might first appear. Adenocarcinomas and squamous cell carcinomas are both classified as non-small cell lung cancers, the most common form of primary lung cancer, but they are thought to arise from different cells of origin and carry distinct genetic profiles. Adenocarcinomas, the most prevalent subtype, often originate from the surfactant-producing cells that line the lungs, while squamous cell carcinomas arise from the cells lining the central airways. Critically, KRAS mutations are found far more frequently in adenocarcinomas than in squamous cell carcinomas. A tumor that abandons its adenocarcinoma identity for a squamous one is, in effect, walking away from the very dependency that the drug was designed to exploit.

To understand how such a transformation could occur, the MIT team, led by graduate student Carrie Rodriguez and Nicolas Mathey-Andrews PhD ’25, with Professor Tyler Jacks of the Koch Institute for Integrative Cancer Research as senior author, engineered a mouse model of lung cancer carrying the precise mutation targeted by the approved inhibitors. When the researchers treated these mice with a KRAS-G12C inhibitor, they found that tumors which had lost the function of a gene called Nkx2-1 were able to undergo the transition from adenocarcinoma to squamous cell carcinoma. Nkx2-1 normally helps maintain alveolar epithelial identity, acting as a guardian of the lung lineage; when it is lost, the cells appear freed from their original identity and can drift toward an alternative fate.

The researchers also identified a second route into the same destination. Turning on a transcription factor called DeltaNp63, which is overactive in many squamous cell carcinomas, made the adeno-to-squamous transition more likely. A third player, the transcription factor SOX2, also helped stimulate the transition, although it could not initiate the process on its own. Together, these findings sketch a regulatory landscape in which the fate of a lung tumor cell is governed by a balance of lineage-defining factors: loss of the lung identity keeper Nkx2-1 on one side, or overexpression of squamous master regulators such as SOX2 or DeltaNp63 on the other, can tip the cell into a new state.

What makes these transformed tumors so dangerous is what the researchers observed about their signaling. The tumors that underwent the tissue transformation did not acquire the mutations that typically boost KRAS expression in adenocarcinomas. Instead, KRAS signaling was shut off, or at least dampened significantly, rendering the inhibitor irrelevant. The cells no longer require the oncogene the drug was blocking, and the team hypothesizes that they switch on alternative signaling pathways that allow them to keep growing. Identifying those pathways is now a central goal of the ongoing work, because they could reveal targets for new drugs capable of preventing or delaying resistance to KRAS inhibitors.

The clinical implications are considerable. Targeted cancer therapies have transformed outcomes in many tumor types, but their Achilles heel has always been the emergence of resistance, and this study adds an important dimension to how that resistance can arise. If a tumor can escape a drug not by mutating the target but by changing what it fundamentally is, then combination strategies may need to account for lineage plasticity as well as classic genetic escape routes. As Rodriguez notes, the main takeaway is that there appear to be different routes of resistance to KRAS inhibitors, and the field needs to think about how to address them. Monitoring tumors for signs of transformation, and developing agents that block the transition itself, could become essential components of future treatment regimens for the many patients whose lung adenocarcinomas harbor KRAS mutations.

There is also a broader scientific payoff. As Mathey-Andrews points out, the adeno-to-squamous transition is a process that remains poorly understood, and the team was encouraged that their models could capture it in the laboratory. The researchers are now digging deeper into what happens inside tumor cells as they shift into a squamous state, hoping to uncover vulnerabilities that could be exploited therapeutically. Future work aimed at translation will use these models to define the conditions under which histologic transformation occurs and to nominate potential downstream targets for drug development. The study was supported in part by the Koch Institute Support Grant from the National Cancer Institute, a Ruth Kirschstein National Service Research Award, the National Institute of General Medical Sciences, and the Ludwig Center at MIT. For patients facing the prospect of relapse after KRAS-targeted therapy, the study offers both a warning and a roadmap: the escape routes are more varied than once believed, but they are now, for the first time, being mapped.

Subject of Research: Mechanisms of resistance to KRAS inhibitors in lung adenocarcinoma through gene amplification and lineage transformation

Article Title: Lung cancers can use two different mechanisms to evade KRAS-inhibiting drugs

Article References: Lung cancers can use two different mechanisms to evade KRAS-inhibiting drugs. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: KRAS inhibitors, lung adenocarcinoma, squamous cell carcinoma, drug resistance, lineage plasticity, Nkx2-1, DeltaNp63, SOX2, MAP kinase pathway, KRAS-G12C, targeted therapy, Nature Genetics

The research team turned to genetically engineered mouse models of Kras-driven lung adenocarcinoma, the workhorse systems that have long defined lung cancer biology. These autochthonous models, in which tumors arise in their natural tissue environment after viral activation of oncogenic Kras, faithfully recapitulate the anatomy and evolution of human disease. When the investigators treated mice bearing Kras G12C tumors with sotorasib, the response was rapid and robust. Micro-computed tomography scans showed aeration returning to compressed lung tissue, and histological analysis confirmed widespread tumor regression. But the response was never complete. Even after two weeks of treatment, residual disease persisted, and it was this residual population that held the clues to what would come next.

Single-cell RNA sequencing of the residual tumors revealed something unexpected. Rather than resembling the aggressive adenocarcinoma cells that dominated before treatment, the surviving cells had shifted toward a transcriptional program resembling alveolar epithelial cells, the specialized gas-exchange cells of the lung. Markers such as HOPX and surfactant proteins became prominent. This finding aligns with a growing body of evidence that alveolar differentiation itself can blunt dependence on KRAS signaling, suggesting that the drug pushes tumors into a state where the oncogene matters less. The residual disease was not simply a smaller version of the original tumor; it was a fundamentally different cellular entity, poised at a lineage crossroads.

What happened under continued treatment was equally revealing. With sustained sotorasib administration, the researchers invariably observed genetic amplification of the Kras oncogene as the dominant resistance mechanism. Using advanced genomic tools, including whole-genome sequencing and computational reconstruction of amplification architecture, the team found that resistant tumors had accumulated extra copies of the mutant Kras allele, in some cases organized on circular extrachromosomal DNA, a notoriously dynamic form of oncogene amplification. Some tumors also amplified Myc or Mycn. This is a classic oncogene-centric escape: the cancer simply makes more of the drug target, overwhelming the inhibitor. In these tumors, MAPK pathway activity, measured by phosphorylated ERK staining, remained evident, confirming that KRAS signaling had been restored.

But oncogene amplification is only one route to resistance. The more provocative question the study addressed is whether tumors can escape KRAS dependence altogether by changing who they are. Histologic transformation, in which an adenocarcinoma converts to a squamous cell carcinoma or even small-cell lung cancer under the pressure of therapy, is a documented phenomenon in patients treated with EGFR and ALK inhibitors. The team used functional CRISPR approaches in their mouse models to deliberately promote squamous lineage transformation and ask whether this change in cellular identity could render tumors indifferent to KRAS inhibition.

The answer, established through a series of elegant experiments, was a clear yes. In alveolar organoid cultures derived from Kras-mutant, p53-deficient lung tissue, forced expression of the transcription factor ΔNp63 was sufficient to reprogram the adenocarcinoma cells into a squamous state. These reprogrammed organoids became strikingly insensitive to KRAS inhibitors, surviving drug concentrations that killed their untransformed counterparts. Critically, the squamous organoids did not show reactivation of KRAS or MAPK signaling when treated. Their resistance was not about reactivating the oncogene; it was about no longer needing it. The drug still hit its target, but the target no longer mattered to the cell’s survival.

In living animals, the team identified the genetic conditions that poise tumors for this fate. Loss of Nkx2-1, the master transcription factor that maintains lung adenocarcinoma identity, facilitated squamous transformation in autochthonous tumors. Ectopic expression of Sox2, the lineage-defining transcription factor of squamous lung cancer, cooperated with Nkx2-1 loss to drive adenosquamous tumors, mixed lesions containing both adenocarcinomatous and squamous components. When mice bearing these transformed tumors were treated with sotorasib for extended periods, the squamous compartments persisted and progressed while showing no evidence of KRAS or MAPK reactivation. Lineage transcription factors, the study concludes, can mediate genuine KRAS independence, a mechanism fundamentally distinct from the amplification-driven resistance seen in adenocarcinomas that retain their identity.

The mechanistic logic of this transformation is rooted in developmental biology. NKX2-1 acts as a guardian of alveolar and pulmonary fate, and its loss releases tumor cells from that commitment, allowing alternative lineage programs to take over. ΔNp63, the dominant-negative isoform of the p53 family member p63, is the molecular switch for stratified epithelial identity, essential for the proliferative potential of basal cells in squamous epithelia. SOX2, meanwhile, has been shown in prior work to be the determining oncogenic switch that promotes lung squamous carcinoma from multiple cells of origin. The new study ties these threads together into a coherent model: the balance between NKX2-1 and factors such as ΔNp63 and SOX2 governs whether a KRAS-mutant tumor remains addicted to its driver or can be reprogrammed into a state where the driver is dispensable.

The clinical implications are substantial. KRAS G12C inhibitors are now approved therapies, but clinical responses are incomplete and resistance is nearly universal, with documented mechanisms including new KRAS mutations, bypass signaling through EGFR and other receptors, and epithelial-to-mesenchymal transition. The mouse models in this study mirror that reality: initial responses were rapid but partial, and residual disease consistently evolved under drug pressure. If a subset of human tumors can achieve resistance through lineage plasticity rather than target reactivation, then combination strategies aimed solely at suppressing MAPK signaling will fail for those patients. Monitoring for lineage markers, such as NKX2-1 loss, ΔNp63 or SOX2 emergence, could identify patients whose tumors are drifting toward KRAS independence before overt progression, and biopsy of resistant lesions may need to look at histology as closely as genomics.

There is also a broader lesson for targeted therapy across oncology. The study echoes patterns seen in EGFR-mutant lung cancer, where squamous and small-cell transformation accompany resistance to osimertinib, often in tumors with RB1 and TP53 alterations. In those contexts too, the transformed tumors frequently lose dependence on the original driver. What this new work adds is a mechanistic, causally tested framework in mouse models: specific transcription factors are sufficient to confer drug resistance by rewriting cellular identity, and the resulting state is stable and heritable. Therapies that target the lineage machinery itself, or that prevent the plastic transition in the first place, may be needed alongside KRAS inhibitors to make responses durable. As KRAS drugs become a cornerstone of lung cancer treatment, this study makes clear that the battle against resistance will be fought not only over the oncogene, but over the very identity of the tumor cell.

Subject of Research: Lineage plasticity and transcription factor-driven squamous transformation as mechanisms of resistance to KRAS inhibitors in mouse models of non-small-cell lung cancer

Article Title: Lineage identity governs oncogene dependence in mouse NSCLC models of KRAS inhibitor resistance

Article References: Mathey-Andrews, N., Rodriguez, C. L., Shui, B., Patriotis, A. L., Rideout, W. M., III, Chen, V. Z., Murazzi, I., Ghazi, P., Cornwall-Brady, M. R., Liu, M., Heileman, M. G., Trakala, M., Concepcion-Crisol, C. P., Yang, D., & Jacks, T. (2026). Lineage identity governs oncogene dependence in mouse NSCLC models of KRAS inhibitor resistance. Nature Genetics. https://doi.org/10.1038/s41588-026-02768-8

Image Credits: AI Generated

DOI: 10.1038/s41588-026-02768-8

Keywords: KRAS inhibitors, lung adenocarcinoma, lineage plasticity, squamous transformation, NKX2-1, SOX2, DeltaNp63, drug resistance, genetically engineered mouse models, targeted therapy, MAPK signaling, histologic transformation

MROH1, also known as HEATR7A, first drew attention from work on the humble roundworm Caenorhabditis elegans. Researchers had identified the worm protein HPO-27, a HEAT repeat protein, as a critical mediator of lysosomal membrane scission. When HPO-27 is lost, the worm’s tissues fill up with aberrant tubular lysosomal networks instead of the usual discrete vesicles. The mammalian homologue MROH1 was subsequently shown to interact with the WASH–actin machinery to regulate lysosomal fission, positioning it as a gatekeeper of lysosomal integrity. What remained entirely unknown was whether this housekeeping role had any physiological relevance for hormone-producing tissues, and no prior study had ever connected MROH1 to thyroid biology.

A crucial clue came from human gene expression databases. Transcriptomic profiling across the GTEx portal and the Human Protein Atlas classifies MROH1 as markedly tissue-enhanced in the thyroid gland relative to other organs—striking preferential expression for a core component of the lysosomal fission machinery. That observation prompted the Tsukuba team, led by Nami Ohuchi and Yoshinori Osaki under the supervision of Hitoshi Shimano, to generate a global MROH1 knockout mouse line. Sperm carrying the Mroh1(tm1a(KOMP)Wtsi) allele were obtained from the European Mouse Mutant Archive, floxed mice were created by Flpe-mediated excision of the gene trap cassette, and ubiquitous deletion of exons 5 through 7 was achieved by crossing with Ayu1-Cre transgenic mice. Cre-negative floxed littermates served as wild-type controls throughout.

The knockout strategy worked as designed: quantitative RT-PCR confirmed the complete absence of Mroh1 transcripts in the thyroids of the deficient animals. To address possible genetic compensation, the team also measured Mroh2a, a close paralog of Mroh1, and found only a non-significant upward trend in its expression. Metabolic phenotyping then produced a subtle but revealing picture. Food intake and body length were unchanged between genotypes, but the knockout mice gained weight gradually, reaching a statistically significant difference by 24 weeks of age. The weight gain occurred independently of altered skeletal growth, suggesting systemic metabolic adaptations rather than a primary effect on development.

The endocrine phenotype emerged clearly when the researchers measured serum hormones. Free thyroxine (FT4) was significantly reduced in knockout mice at both 3 and 6 months of age, while free triiodothyronine (FT3) was significantly lower by 6 months. Serum TSH showed only a non-significant increasing trend—a puzzling feature the authors openly acknowledge, since standard rodent thyroid economy would predict a compensatory TSH rise when circulating hormones fall. Whether the discrepancy reflects altered central feedback, differences in hormone metabolism, or transport effects remains unresolved and will require functional assessment of the hypothalamic–pituitary axis in future work.

Consistent with the well-known clinical association between hypothyroidism and dyslipidemia, total serum cholesterol was comparable at 3 months but significantly elevated in the knockout animals by 6 months, while triglycerides remained unchanged. Importantly, markers of liver and kidney function, blood glucose, and creatine kinase levels were all unremarkable, and histological examination of the lung, brain, liver, and skeletal muscle revealed no overt abnormalities. The thyroid, in other words, stood out as the principal site of pathological consequence—an outcome that mirrors MROH1’s preferential expression in that gland and strengthens the causal narrative.

To understand the structural basis of the hormone deficit, the team turned to histology. At 3 months of age, thyroid morphology in the knockout mice looked essentially normal. By 6 months, however, the gland showed clear architectural remodelling: follicular area was reduced, and follicles were progressively replaced by interstitial cells and adipocyte-like structures. Quantification of the follicle area ratio showed a downward trend that narrowly missed statistical significance, but a more sensitive analysis of individual follicles—over 1,700 follicles measured across both groups—revealed a statistically significant shift towards smaller follicle sizes in the knockout mice (p = 0.0095, Kolmogorov–Smirnov test). The gland, in effect, was quietly remodelling itself at the cellular level long before gross pathology would appear.

Molecular profiling pointed to the transcriptional roots of the defect. Expression of Nkx2-1 and Foxe1, the master regulators of thyroid differentiation, was significantly reduced in the knockout thyroids, with Pax8 and Hhex trending in the same direction. Concurrently, thyroglobulin—the essential precursor of thyroid hormone synthesis—was significantly downregulated, as was Slc16a2 (Mct8), the thyroid hormone transporter. Other genes involved in hormone production, including Tshr, Slc5a5 (Nis), and Slc26a7, showed decreasing trends. This coordinated loss of lineage-defining transcription factors and their functional target genes suggests that MROH1 is required for the long-term maintenance of follicular cell identity and differentiated function, not merely for organelle housekeeping.

What the study did not find is equally telling. Given MROH1’s established role in lysosomal fission and the dependence of hormone release on lysosomal proteolysis, the team fully expected to find impaired lysosomal function. Instead, immunoblotting showed that protein levels of LAMP2, cathepsin L, and cathepsin D were unchanged, and two independent assays—a live-cell fluorogenic substrate assay in primary thyroid cells and an enzymatic activity assay in whole-tissue lysates—revealed no significant difference in cathepsin L activity. The fundamental capacity for lysosomal degradation appeared intact. The authors caution that bulk assays may simply be too blunt to detect localized defects in lysosomal membrane trafficking, and that subtle, progressive endo-lysosomal trafficking failures could still accumulate over time, as seen in the delayed thyroid pathology of lysosomal storage disease models such as cystinosis.

The broader significance is twofold. First, the work establishes MROH1 as a genetic factor for thyroid hormone homeostasis in vivo, with a phenotype distinct from the profound hypothyroidism and goitre seen in complete MCT8 or thyroglobulin knockouts—the partial downregulation of thyroid genes produces a milder, late-onset endocrine defect without gland enlargement. Second, it extends the emerging view that lysosomal membrane dynamics are not merely cellular plumbing but active participants in tissue-level physiology, with the caveat that the precise mechanistic bridge from MROH1 deficiency to transcriptional downregulation remains to be charted. Because the mice carry a congenital deletion yet show a late-onset phenotype, extrathyroidal contributions cannot be excluded. Tissue-specific knockout models, currently the next step for the Tsukuba group, should disentangle the global versus thyroid-specific roles of MROH1—and may ultimately clarify whether subtle lysosomal trafficking defects in humans contribute to mild hypothyroidism, thyroid remodelling, and the cardiovascular risk that follows from unexplained hypercholesterolemia.

Subject of Research: The role of the HEAT repeat protein MROH1 in lysosomal fission and thyroid hormone homeostasis in mice

Article Title: The HEAT Repeat Protein MROH1 Deficiency Leads to Reduced Circulating Thyroid Hormone Levels in Mice

Article References: Ohuchi, N., Osaki, Y., Nakagawa, Y., Miyamoto, T., Araki, M., Mizunoe, Y., Matsuda, T., Murayama, Y., Sugano, Y., Iwasaki, H., Matsuzaka, T., Sekiya, M., & Shimano, H. (2026). The HEAT Repeat Protein MROH1 Deficiency Leads to Reduced Circulating Thyroid Hormone Levels in Mice. Endocrinology, Diabetes & Metabolism, 9(5), Article e70348. https://doi.org/10.1002/edm2.70348

Image Credits: AI Generated

DOI: 10.1002/edm2.70348

Keywords: MROH1, thyroid hormone, lysosomal fission, hypothyroidism, hypercholesterolemia, knockout mice, Nkx2-1, Foxe1, thyroglobulin, cathepsin L, endocrine physiology, University of Tsukuba