Tumor laterality in primary intestinal diffuse large B-cell lymphoma: A prognostic leap or an anatomical mirage?

Abstract

Primary intestinal diffuse large B-cell lymphoma (PI-DLBCL) is a heterogeneous entity for which the International Prognostic Index offers suboptimal risk stratification. Drawing from the prognostic significance of tumor sidedness in colorectal cancer, recent research has explored whether anatomical laterality influences survival in PI-DBLCL. Previous research has identified left-sided PI-DLBCL as an independent poor prognostic factor and developed a superior laterality-integrated nomogram. In this opinion review, we dissect the methodological limitations, including its reliance on registry data lacking critical molecular and treatment variables, and the modest clinical magnitude of the laterality effect. We then delve into the plausible biological mechanisms underpinning this observation, such as embryologic, microbiomic, and immunological gradients along the intestinal axis, which may shape a distinct tumor microenvironment. Finally, we outline a future research agenda. While tumor laterality is a valuable supplementary prognostic indicator, it currently serves more as a “mirage” than a “leap” for guiding treatment. The path forward requires prospective, biologically annotated cohorts integrating spatial biology, multi-omics, and novel technologies like radiomics and spatial transcriptomics to translate this anatomical observation into clinically actionable insights for personalized management of PI-DLBCL.

Key Words: Primary intestinal diffuse large B-cell lymphoma; Tumor laterality; Prognosis; Spatial biology; Tumor microenvironment; Gut microbiome

Core Tip: The observation that left-sided primary intestinal diffuse large B-cell lymphoma (PI-DLBCL) carries a worse prognosis than right-sided disease introduces a novel anatomical paradigm into lymphoma risk stratification. While intriguing, this finding’s clinical utility is currently limited by modest effect sizes and a lack of mechanistic understanding. This opinion review argues that tumor laterality is best viewed not as an immediate treatment-guiding tool, but as a powerful lens through which to explore the spatial biology of PI-DLBCL. Future research must move beyond anatomical correlation to elucidate the underlying microbiomic, immunologic, and molecular drivers, paving the way for truly personalized therapeutic strategies.

INTRODUCTION

Primary intestinal diffuse large B-cell lymphoma (PI-DLBCL) represents a clinically heterogeneous subset of extranodal lymphomas, posing significant challenges for accurate prognostication. The International Prognostic Index (IPI), a cornerstone for nodal diffuse large B-cell lymphoma (DLBCL), demonstrates suboptimal performance in PI-DLBCL as it fails to capture the unique anatomical and microenvironmental complexities of the gastrointestinal tract[1-4]. This prognostic gap has spurred the search for novel, disease-specific biomarkers.

In a pioneering effort to bridge this gap, Zeng et al[5] recently investigated the prognostic value of a seemingly simple anatomical variable: Tumor laterality. Borrowing a well-established concept from colorectal adenocarcinoma, where right- and left-sided tumors exhibit distinct biological behaviors and outcomes, they queried whether the splenic flexure could serve as a prognostic boundary in PI-DLBCL. Using the Surveillance, Epidemiology, and End Results (SEER) registry for model development and an institutional cohort for validation, they reported that left-sided PI-DLBCL was independently associated with inferior overall survival [hazard ratio (HR) = 1.15, P = 0.035]. Furthermore, their laterality-integrated nomogram outperformed the traditional IPI[5,6].

This study is commendable for its innovative translation of a “spatial biology” concept from solid tumors to lymphoid malignancies. However, its findings raise more questions than they answer, prompting a critical evaluation of their clinical significance and biological foundation. Is tumor laterality a genuine “prognostic leap” that should refine our clinical approach, or is it an “anatomical mirage”—a statistically significant but clinically modest observation that distracts from more powerful biological determinants? This opinion review will explore the potential biological mechanisms that could underlie the prognostic impact of laterality, and propose a roadmap for future research to transform this intriguing anatomical clue into a clinically actionable paradigm (Figure 1).

Figure 1 Conceptual framework illustrating the transition from the current evidence for tumor laterality in primary intestinal diffuse large B-cell lymphoma (left) to the proposed future research roadmap (right). The “anatomical mirage” reflects methodological limitations, modest clinical effect size, and lack of mechanistic insight, whereas the “prognostic leap” emphasizes biologically annotated cohorts, cutting-edge spatial and microbial technologies, and translation into personalized therapeutic strategies. This framework highlights the necessity of moving beyond retrospective anatomical correlation toward integrated multi-dimensional biology. PI-DLBCL: Primary intestinal diffuse large B-cell lymphoma; SEER: Surveillance, Epidemiology, and End Results; IPI: International Prognostic Index; LDH: Lactate Dehydrogenase; HR: Hazard Ratio.

THE PROGNOSTIC PUZZLE: STATISTICAL SIGNIFICANCE VERSUS CLINICAL IMPACT

The study by Zeng et al[5] provides a compelling statistical case for the independent prognostic value of tumor laterality in PI-DLBCL. The finding that left-sided disease confers a 15% increased risk of death (HR = 1.15) is robust within their model and was validated in an external cohort. The development of a nomogram that integrates laterality with established factors like age, stage, and treatment represents a valuable step toward more personalized risk visualization. However, several critical limitations temper the initial enthusiasm and underscore the need for cautious interpretation.

Methodological caveats

The study’s foundation on the SEER database, while providing a large sample size, introduces inherent limitations. The absence of key prognostic variables is a major drawback. Critically missing data include serum lactate dehydrogenase (LDH) levels, performance status, and the presence of B symptoms—all core components of the IPI and its enhancements (NCCN-IPI)[1]. More importantly, the complete lack of molecular data is a significant weakness in the modern era. Tumor biology, as defined by cell-of-origin [germinal center B-cell (GCB) vs non-GCB], double-expressor status, and genetic mutations (e.g., MYD88 and CD79B)[7,8], is now recognized as a primary driver of outcomes in DLBCL, often overshadowing clinical factors[9-11]. Without these data, it is impossible to determine if laterality is an independent prognostic factor or merely a surrogate for an unequal distribution of these powerful biological subtypes. The substantial cohort imbalance (474 left-sided vs 3358 right-sided) further challenges the statistical stability of the findings for the smaller left-sided group.

The modest clinical magnitude

The reported HR of 1.15 for left-sided disease, while statistically significant, is clinically modest. This is starkly contrasted by the impact of treatment itself: The absence of chemotherapy in their model was associated with a much higher HR of 1.80[5]. This reinforces that the backbone of therapy—modern immunochemotherapy like R-CHOP—remains the dominant modifiable prognostic factor[2,12]. Therefore, from a clinical decision-making perspective, the presence of left-sided disease alone does not, and should not, warrant a deviation from standard, guideline-recommended therapy. As highlighted in a recent Journal of Clinical Oncology meta-analysis, survival in gastrointestinal lymphomas is far more strongly linked to molecular features and treatment adherence than to primary subsite alone[13].

In essence, Zeng et al[5] have identified a signal. But its weakness, coupled with the methodological noise from unmeasured confounders, suggests that it is a signal that is unlikely to be heard above the din of more potent biological drivers in a real-world clinical setting. Its current utility lies not in dictating therapy, but in refining prognostic discussions and generating hypotheses for future trials.

UNMASKING THE MIRAGE: THE QUEST FOR BIOLOGICAL PLAUSIBILITY

If laterality is more than a statistical artifact, what are the biological mechanisms that could explain the survival difference between right- and left-sided PI-DLBCL? Zeng et al[5] rightly hypothesize that the answer lies in the distinct embryologic, microbiomic[14-16], and immunological milieus along the intestinal axis, a concept extensively studied in colorectal cancer[17-20].

The immune landscape

The right and left colon arise from the midgut and hindgut, respectively, and are populated by distinct microbial communities. This, in turn, shapes a divergent local immune environment. The right colon is characterized by a higher density of IgA⁺ B cells and regulatory T cells (Tregs), potentially fostering a more tolerogenic or distinct lymphomagenic niche. In contrast, the left colon exhibits lower microbial diversity and is often enriched for pro-inflammatory, genotoxic bacteria like Fusobacterium nucleatum (F. nucleatum) and enterotoxigenic Bacteroides fragilis[21-23].

The microbial-cell-of-origin axis

This microbial dichotomy could directly influence lymphoma biology. For instance, F. nucleatum can activate the TLR4/MYD88 signaling pathway, which is recurrently mutated and oncogenic in the activated B-cell subtype of DLBCL[11,24]. It is plausible that left-sided tumors, bathed in a pro-inflammatory microbial milieu, are more likely to originate from or be driven towards this more aggressive, non-GCB phenotype. This could provide a mechanistic link between anatomical location and the poor outcomes associated with left-sided disease. A seminal study by Yoon et al[25] in Blood demonstrated that gut microbial[26-29] dysbiosis influences both the efficacy and toxicity of immunochemotherapy in DLBCL, providing a powerful precedent for this line of inquiry[30-33].

A hypothesis, not a conclusion

While biologically plausible, these mechanisms remain entirely hypothetical for PI-DLBCL. Zeng et al[5] provided no direct evidence, such as 16S rRNA sequencing of tumor-associated microbes or immunohistochemical profiling of immune cell subsets. The observed survival advantage of right-sided PI-DLBCL over intra-abdominal nodal DLBCL further complicates the picture. Without controlling for tumor biology, this could simply reflect a higher prevalence of favorable GCB subtype or more complete surgical resection in right-sided lesions, rather than an inherent biological advantage. The true value of the laterality finding is not as a final answer, but as a compelling hypothesis-generator, redirecting our focus toward the spatial[34-37] and microbial dimensions of lymphomagenesis[38-40].

FROM ANATOMICAL MIRAGE TO THERAPEUTIC LANDMARK: A FUTURE RESEARCH AGENDA

To transform the “anatomical mirage” of laterality into a genuine “prognostic leap”, the field must move beyond retrospective registry analyses and embrace a prospective, multi-dimensional research framework. We propose a roadmap centered on three key pillars.

Prospective, biologically annotated cohorts

The next critical step is the establishment of large, multicenter, prospective cohorts of patients with PI-DLBCL. These cohorts must systematically collect not only clinical data (LDH, stage, performance status, and B symptoms) and detailed treatment information (regimen, dose intensity, and cycles), but also a comprehensive biospecimen repository. This should include: (1) Tumor tissue: For centralized pathology review, cell-of-origin determination (by Hans algorithm or gene expression profiling), assessment of double-expressor/double-hit status, and targeted next-generation sequencing for recurrent mutations (e.g., MYD88, CD79B, BCL2, and MYC)[7,8,11]; (2) Microbiome sampling: Collection of fecal samples and/or tumor-adjacent mucosal biopsies for 16S rRNA and metagenomic sequencing to characterize the gut[14,21,25-27] and tumor microbiome[28-32]; and (3) Immune profiling: Multiplex immunohistochemistry or flow cytometry to map the composition and spatial organization of the tumor immune microenvironment[34-37] in both right- and left-sided tumors[38-40].

Such a resource would allow for robust multivariable analyses to determine if laterality remains an independent prognostic factor after controlling for these powerful biological variables, or if its effect is entirely mediated by them.

Leveraging cutting-edge technologies

The complexity of the gut ecosystem demands sophisticated tools. Future studies should harness: (1) Spatial transcriptomics: This technology can simultaneously map gene expression within the tissue architecture, revealing how gradients of microbial metabolites, immune cells, and lymphoma cells interact along the intestinal axis. It could identify unique “spatial signatures”[41-43] associated with right- vs left-sided tumors that correlate with treatment response and survival[44-46]; (2) Radiomics: Pre-treatment computed tomography (CT) or positron emission tomography/CT scans contain a wealth of quantitative data beyond simple tumor size and location. Radiomics can extract thousands of features related to tumor texture, shape, and heterogeneity, potentially capturing non-invasive surrogates for underlying tumor biology and the surrounding microenvironment. A radiomic signature of laterality[47-50] could offer a readily available prognostic tool[51-53]; and (3) From prognosis to prediction: The ultimate goal is to move beyond prognostic association to predictive utility. Does laterality predict response to specific therapies? For example, could left-sided tumors, potentially driven by a Fusobacterium-TLR4-MYD88 axis, be more susceptible to BTK inhibitors[11,24,54-56] (e.g., ibrutinib) or agents that modulate the microbiome[57-61]? Future clinical trial designs should consider laterality as a potential stratification factor. This would allow for exploratory analyses to determine if patients with left-sided PI-DLBCL derive a differential benefit from treatment intensification or the addition of novel agents, compared to their right-sided counterparts.

CONCLUSION

The study by Zeng et al[5] has performed a valuable service by introducing the concept of spatial biology into the prognostication of PI-DLBCL. It has challenged us to look beyond traditional clinical and pathological factors and consider the fundamental influence of the anatomical “soil” in which these lymphomas arise. Tumor laterality is an independent prognostic factor, but its current clinical impact is modest, serving more as an “anatomical mirage”—an intriguing observation that beckons us forward but does not yet offer a clear path for therapeutic action. The true legacy of this work will not be the nomogram that it produced, but the research agenda that it inspires. The journey from anatomical correlation to biological understanding and clinical utility is just beginning. By integrating rigorous prospective cohort studies with powerful new technologies like spatial transcriptomics and advanced microbiome analysis, we can unmask the biological drivers behind this anatomical observation. Only then can we determine if the “mirage” of laterality will resolve into a genuine landmark, guiding us toward more precise, personalized, and effective management of patients with PI-DLBCL.