Hepatic Progression of Hepatocellular Carcinoma

*Anna Rossetto, Alessandro Rosignoli, Brunilda Tatani, Valli De Re and Alessandro Uzzau*

#### **Abstract**

Hepatocellular carcinoma constitutes an ongoing challenge due to its incidence and the high mortality related to it. Metastases and relapses even after treatment with curative intent are frequent. The liver is a common site for metastasis because of anatomical and physiological reasons; its position, the particular cytoarchitecture and cell populations, and its peculiar immunologic properties make it a favorable and tolerogenic environment; the inflammatory state with the alteration of the cytoarchitecture and of the microcirculation associated, and gut permeability and metabolic diseases cause the development of a liable site to progression of hepatocellular carcinoma. The difficulty of always having an early diagnosis and the lack of therapeutic flow charts including the biological behavior of the disease have always posed great difficulties in dealing with it. In the last few years, mechanisms involved in the onset and in the progression of hepatocellular carcinoma are a source of great interest; the discovery of pro-neoplastic and pro-metastatic conditions, of the cross talk between organs and cells, of progression pathways, of mediators contributing to proliferation and metastasis and of modular check points, of miRNAs, all potential therapeutic targets, appear promising for transforming the approach to hepatocarcinoma, offering the possibility of earlier diagnosis, customizable treatments, and better outcome.

**Keywords:** hepatocellular carcinoma, liver metastasis, hepatic progression of hepatocellular carcinoma, immunotolerance, ischemia/riperfusion injury, miRNAs

#### **1. Introduction**

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death. Locoregional treatment, surgical resection, and liver transplantation are main and most efficient treatments, but the risks of recurrence and metastasis are very high (70% after primary liver resection with curative intent) [1].

The risk of recurrence in HCC is high because of the biological and morphological nature of the liver.

Recurrent disease includes both intrahepatic metastasis, which usually form within the first 2 years of diagnosis, and de novo cancer that generally occurs later. The hepatic vascular anatomy and immunological characteristics create a

pro-neoplastic niche for metastasis, while the continuing damage to the liver creates pro-neoplastic sites susceptible to secondary tumors. Liver metastasis represents a big challenge in the battle against cancer because they have a high mortality rate. Around 30–70% of patients die with liver metastasis, and metastasis is responsible for more than 90% cancer mortality [1].

The position of liver, near the gastrointestinal tract, only partially justifies the metastasis toward it. In fact, for other types of "distant" cancer, the liver is the first and sometimes even the only target of metastasis (e.g., uveal melanoma and triplenegative breast cancer). This consequently suggests that the criterion of proximity is only partially a predisposing factor but rather that there are specific tumor and extra tumor elements that predispose to metastasization to the liver. Another factor that has emerged in recent years is the exchange of information and the "preconditioning" of the liver that occurs before the actual establishment of metastatic colonies.

However, the development of knowledge on the local and systemic factors that promote the advance of the neoplastic disease and favor its metastasis has thus highlighted multiple and rich pathways that are fascinating from a speculative point of view but above all promising for the development of future preventive and therapeutic strategies.

#### **2. Peculiar liver characteristics**

The liver is the only organ with double arterial and venous vascularization. It constitutes the first filter for all effluent blood from the gastrointestinal district. The cytoarchitecture with the lobular arrangement, the portal spaces, and the intricate network of discontinuous capillaries (sinusoids) constitutes a unique feature. Multiple cell populations with their pathophysiological implications are responsible of a myriad of actions including favoring or not, the development of metastases.

The cellular structure of the liver is composed of 70% hepatocytes and 30% from non-parenchymal cells, which are crucial in the activation of many very characteristic liver phenomena.

#### **2.1 Hepatic stellate cells**

In a physiological condition, the stellate cells represent 1.5% of the entire hepatic parenchyma and 1/3 of the non-parenchymal cell compartment. They have multiple functions, from the ability to store lipids and vitamin A, to their involvement in the reparative phenomena of the hepatic parenchyma, fibrinogenesis, and the maintenance of homeostasis. They have intrahepatic and subendothelial cytoplasmic extensions through which they can establish connections with hepatocytes; are sensitive to the chemotactic stimulus and respond to alpha adrenergic activation. They are activated following the inflammatory stimulus, losing their lipid vacuoles, and developing microfilaments evolving into myofibroblasts. They play a key role in fetal hepatic development, become fundamental in the phenomena of hepatic regeneration of the adult liver and in the remodeling of the extracellular matrix through the secretion of angiogenetic factors, cytokines (IL-6, IL-10, TGF-β), adhesion molecules, connective tissue growth factor (CTGF), Endothelin-1, contributing to the activation of endothelial cells and facilitating the extravasation of neoplastic cells in the liver and supporting metastasizing [1].

*Hepatic Progression of Hepatocellular Carcinoma DOI: http://dx.doi.org/10.5772/intechopen.106169*

They can undergo the mesenchymal-to-epithelial transition and thus become liver progenitor cells giving rise to hepatocytes. They also play an important action at the immunological level as they can act as antigen receptor cells (APCs), receive stimuli from leukocytes, support leukocyte recruitment and activation, modulate the intensity of the activation of the immune response. They are the main cell type involved in fibrogenesis in response to liver damage [2].

#### **2.2 Kupffer cells (KCs)**

They represent 20–30% of non-parenchymal cells. They are liver-derived macrophages that support both innate and adaptive immune responses to pathogens originating from the gastrointestinal tract through the effluent blood arriving via the portal vein. They are activated through two types of polarization, classical (M1), when stimulated by IFN, TNF, GM-CSF, or mycrobic stimuli or alternative (M2) when stimulated by IL-4, IL-13 and IL-33. They perform important functions in the mechanism of liver damage, in ischemic/reperfusion injury, in alcoholic liver disease, in nonalcoholic fatty liver disease, in immunotolerance phenomena after liver transplantation, and in endotoxin tolerance modulation. In response to the inflammatory stimulus, they are involved in the activation of HSCs, thus promoting fibrosis through the release of mediators (TGF-beta and platelet-derived growth factor).

Hepatic sinusoid stromal cells, hepatic sinusoidal endothelial cells, and stellate cells are the first liver cells to come into contact with systemic antigens and derived from the gastrointestinal tract [1, 3, 4].

#### **2.3 Immunotolerance**

Another fundamental aspect is its function as a tolerogenic immunosuppressive organ toward the molecules absorbed by the intestine and therefore, at the same time, the tumor cells and infectious agents. The liver contains numerous immune system cells, both adaptive and innate, specialized in the recognition and capture of infectious agents with the recruitment of inflammatory and leukocyte cells and the presentation of antigens to lymphocytes in the bloodstream. However, this mechanism must be finely controlled so that the immune response is not implemented toward non-pathogenic molecules such as those of the host or deriving from ingested food. It is this balance between activation of the immune response and its inhibition characterizes the liver as the main organ of the host's first immune barrier [5–7].

The idea that the immune system plays an important role in the development of neoplastic pathology is dated and has been controversial for years; however, several studies on transplants have expanded knowledge about tolerance since the ability to induce tolerance toward the transplanted organ is essential for the survival of the graft.

While it is clear that through the oral route and the gastrointestinal system tolerance can be induced through the local activation of the gastrointestinal immune system, it is, however, shown that much of the induction of the tolerance process takes place in the liver. In particular, survival of the graft in liver transplantation has been demonstrated in subjects without kinship ties of some animal species without immunosuppression and still in some cases in which the expression of a tolerant phenotype allowed the suspension of immunosuppressive therapy [8, 9].

The hepatic parenchyma therefore has very important immunological functions and the peculiar ability to induce tolerance: the activation of the liver immune system, consisting of macrophages, dendritic cells, natural killer, and T lymphocytes, produces immunological mediators (in particular IL 10, TGF beta, and others), which, on the one hand, induce localized immunological suppression aimed at minimizing liver damage, on the other create a tolerant environment for the colonization of metastatic clones. Both sinusoidal endothelial cells and stellate cells activated by TGF-beta and PDGF are strongly involved in the maintenance of local and systemic tolerance phenomena. In addition, the same T lymphocytes made tolerant are then able to return to the primary tumor and suppress the local defense systems [6–12].

The involvement of the immune response and immunocompetence in the development of neoplastic diseases has been, and still is, a subject of debate, because many of the tumor antigens are self-antigens for which the immunological response is weaker and more difficult to measure. However, it is well known that individuals with a decline in immune defenses related to old age, or undergoing immunosuppressive therapies, or suffering from immune system disorders such as chronic infections or autoimmune diseases have an increased risk for the development of metaplasia; even the most common and recognized risk factors for cancers such as smoking, alcohol abuse, advanced age, and poor nutritional status are associated with more or less pronounced alterations of the immune system and risk of metastasis [13].

#### **2.4 Cancer-derived microvescicles**

Cancer-derived microvesicles have recently been identified as responsible for very important roles at the level of the tumor microenvironment, contributing through their load to the development of metastases and to the selection of organotropism. The microvesicles produced by the tumor cells are released into the circulation before the cancer cells reach metastatic sites.

The information transmitted by them is able to initiate a congenial soil phenomenon (as claimed in Paget's theory) starting processes of angiogenesis, cancer-associated fibroblasts (CAFs) formation, endothelial cell migration.

The signal mediated by microvesicles allows an exchange of intracellular information with the possibility of modulating the migratory and metastatic behavior of more quiescent cells but also of inducing drug resistance. They are also able to reduce the immune response by increasing the development of immunosuppressive cell populations (PD-1 positive nonclassical monocyte) reprogram the cellular metabolism of neoplastic cells, which is a fundamental step in the extravasation and dissemination of tumor cells.

In the studies of the last few years, it appears increasingly evident that the target organs for the development of metastases undergo phenomena that define their receptivity and mediated by the primary tumor well before the development of metastases.

At the hepatic level, the extracellular vesicles produced by the neoplastic cells first interface with the Kupffer cells. The information deriving from the EVs affects the hepatic stromal cells with the consequent activation of hepatocyte growth factor, which favors the development of fertile soil for the development of metastases [14–17].
