The Neoplasia as embryological phenomenon and its implication in the animal evolution and the origin of cancer. I. A presentation of the neoplastic process and its connection with cell fusion and germline formation

1. Problem Statement

The paper addresses a fundamental gap in evolutionary biology and oncology: the lack of a unified theoretical framework explaining the rapid emergence of animal multicellularity (Metazoa) and the simultaneous origin of cancer.

• The Evolutionary Gap: Traditional models often view the transition from unicellularity to multicellularity as a slow, gradual process. However, the authors argue that the formation of the first animal embryo was a rapid, intense event requiring complex cellular coordination (e.g., epiboly, invagination, EMT) that cannot be explained solely by gradual genetic adaptation.
• The Oncological Paradox: Cancer is typically viewed as a disease of somatic mutation and uncontrolled growth. The authors challenge the dogma that cancer is purely a pathological deviation, proposing instead that the mechanisms driving cancer (neoplasia) are the same evolutionary forces that constructed the animal body plan.
• The Core Question: How did the "neoplastic process" (characterized by uncontrolled proliferation, invasion, and migration) become co-opted to create the structured, organized animal embryo, and why do these two opposing states (embryo vs. cancer) share the same molecular machinery?

2. Methodology

This paper is a theoretical review and hypothesis formulation rather than an empirical study with new experimental data. The authors employ:

• Comparative Phylogenetics: Analyzing the life cycles and genomic features of unicellular Holozoa (specifically Ichthyosporea, Filasterea, and Pluriformea) and basal metazoans (ctenophores, sponges) to identify conserved molecular pathways.
• Literature Synthesis: Integrating findings from embryology, biophysics, genomics, and oncology. Key areas of synthesis include:
  • The role of cell fusion and anisogamy in protists.
  • The conservation of "cancer genes" (e.g., Myc, Src, Ras, Abl) in unicellular ancestors.
  • The mechanics of chromatin organization (Topologically Associating Domains - TADs) and mechanotransduction.
• Conceptual Modeling: Proposing the "Neoplastic Functional Module" (NFM) and the "Neoplastic Process" (NP) as evolutionary units that were recruited (co-opted) during the origin of Metazoa.

3. Key Contributions and Hypotheses

A. The Neoplastic Functional Module (NFM)

The authors propose that a pre-existing functional module in unicellular Holozoa, comprising genes associated with proliferation, invasion, adhesion, and metabolism (often termed "cancer genes" in modern contexts), was recruited to form the first embryo.

• Recruitment/Co-option: Instead of new genes evolving, existing unicellular pathways were co-opted. For example, Myc and Ras regulated ribosome biogenesis and motility in protists but were recruited to drive embryonic growth and morphogenesis.
• Duality: The NFM contains dual forces:
  1. Expansive Force: Proliferation and migration (neoplastic drive).
  2. Restraining Force: Tumor suppressors (e.g., p53, Hippo) and adhesion molecules (e.g., cadherins) that act as brakes to organize the expansion.
• Equilibrium: The animal embryo is the result of a dynamic equilibrium between these expansive and restraining forces. Cancer is defined as the re-emergence of the uncontained expansive force when this equilibrium is broken.

B. The Role of Biophysics and Mechanics

A central contribution is the emphasis on biophysics over pure genetics.

• Mechanotransduction: The formation of the embryo was driven by physical forces (tension, substrate stiffness, cell fusion) that altered gene expression via the 3D architecture of the nucleus.
• Mechanical Memory: Physical stimuli during the first embryogenesis (e.g., epiboly, invagination) created a "mechanical memory" stored in chromatin structure (TADs, loops, histone modifications like H3K9me3). This memory allows the embryo to reconstruct its form in subsequent generations.
• Cell Fusion: The authors argue that the first embryo arose from the fusion of phenotypically different cells (anisogamy) in unicellular Holozoa, creating a polyploid/syncytial zygote that triggered the NFM.

C. The Germline and Soma Connection

The paper challenges the strict separation between the germline and soma.

• Fluid Boundary: In basal metazoans (like ctenophores), the germline is not segregated early but arises from multipotent cells later in development.
• Soma-to-Germline Transition: The authors suggest that tumorigenesis involves a "soma-to-germline transition," where somatic cells reactivate germline programs (neoplastic processes) to regain totipotency and proliferative capacity.
• Mos Protein: The proto-oncogene Mos is highlighted as a critical regulator linking meiosis, endomitosis, and the establishment of the germline, suggesting it played a key role in managing polyploidy during the first embryogenesis.

D. Re-evaluating Phylogeny

The authors challenge the view that choanoflagellates are the direct ancestors of metazoans. Instead, they propose that Ichthyosporea, Filasterea, and Pluriformea are closer to the metazoan lineage due to their complex life cycles involving syncytial stages and anisogamy, which better fit the requirements for the NFM recruitment.

4. Results (Theoretical Findings)

While no new experimental data is presented, the paper synthesizes existing data to support the following conclusions:

1. Origin of Cancer Genes: Genes like Myc, Src, Ras, and Abl existed in unicellular ancestors for sporulation and motility, not cancer. Their "cancerous" behavior is a consequence of their recruitment into the NFM without the full context of multicellular regulation.
2. Cancer as an Evolutionary Echo: Cancer is not a random mutation event but the "unveiling" of the ancestral neoplastic force that built the animal body. The immune system's inability to fully eradicate cancer is attributed to the fact that cancer cells reactivate intrinsic, evolutionarily conserved programs essential for animal existence.
3. Rapid Evolution: The NFM model explains the "Cambrian explosion" and rapid radiation of animal forms. The co-option of a pre-existing, powerful neoplastic module allowed for the rapid generation of complex body plans, rather than slow, step-by-step adaptation.
4. Teratocarcinoma as Evidence: The ability of teratocarcinomas to differentiate into benign, organized tissues (embryoid bodies) supports the hypothesis that the neoplastic force contains the blueprint for embryonic organization.

5. Significance and Implications

• Paradigm Shift in Oncology: The paper proposes a shift from viewing cancer solely as a genetic disease of mutation to viewing it as a developmental disorder resulting from the dysregulation of ancient, conserved embryological programs.
• New Therapeutic Avenues: If cancer is a reactivation of embryonic programs, cures may lie in "re-regulating" malignant stem cells back to a benign state using principles of embryonic induction and growth factors (as suggested by G. Barry Pierce), rather than just killing cells via cytotoxicity.
• Evolutionary Biology: It provides a mechanism for the rapid emergence of multicellularity, linking physical forces (biophysics) directly to genetic regulation (epigenetics) via the NFM.
• Interdisciplinary Integration: The work bridges embryology, physics, and oncology, suggesting that the 3D nuclear architecture and mechanical forces are as critical to evolution and disease as the DNA sequence itself.

In summary, the authors argue that Neoplasia is the evolutionary engine that drove the formation of the first animal embryo. Cancer is the "shadow" of this engine—the same force that creates life, but when uncontained by the structural coherence of the embryo, it manifests as disease. Understanding the embryo and cancer as two sides of the same coin is essential for understanding animal evolution and developing new cancer therapies.