FormalPara Key Summary Points

Hepatocellular carcinoma (HCC) is a global killer with preponderance in Asian and African regions. It poses a challenge for successful management in less affluent develo** countries like India, with large populations and limited infrastructures.

This review aims to assess the available options and future directions for management of HCC. It describes current and emerging strategies for detection, staging and therapy of the disease emphasizing measures involving clinical use of radiation.

Using the widely accepted Barcelona Clinic Liver Cancer (BCLC) staging system as a base, it discusses different therapeutic approaches and their synergistic combinations in the context of a patient-specific dynamic results-based strategy, considering multiple HCC management consensus recommendations.

The review has a special focus on radiant therapies that can help downstage intermediate/advanced disease or extend patient lifespan while awaiting other therapies. Such therapies can be made more widely available through development of indigenous formulations and facility installations.

It also discusses the logistical and economic feasibility of these approaches in the context of the limitations of the burdened public health infrastructure in nations like India.

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Introduction

Most major organ functions can at least hypothetically be substituted or supplemented by artificial means, but the liver is such a multi-functional powerhouse—purifying the blood, providing compartmentalized metabolism and directed transport of a vast array of substances, secreting metabolic regulators as well as vital proteins and hormones—that it is as yet impossible for a being to survive any meaningful span without a functioning liver [1]. This supposition is borne out by the fact that liver disease accounts for approximately 2 million deaths per year globally, of which half is attributed to viral hepatitis and hepatocellular carcinoma [2]. This review attempts to provide an overview on the current global status of liver cancer. It also discusses the modalities available for its detection, staging and clinical management, and the feasibility of their application in vulnerable countries like India. A special emphasis is made on radiation-based modalities that can be made locally available to serve the greatest fraction of the affected population.

Hepatocellular Carcinoma—A Cause for Serious Concern

Liver cancer is the fifth most common cancer globally and the third most frequent cause of cancer-related death overall (second for men, sixth for women) [3, 5, 6]. In regions of greater prevalence (Asia, sub-Saharan Africa), HCC is present in > 50% of cases associated with endemic hepatitis B virus (HBV) infection. China, with ~ 84 million infected with HBV, accounts for roughly half of the primary liver cancer incidence in the world [7]. India has ~ 43–45 million chronic HBV sufferers [8], and the reported HCC incidence ranges from 0.7 to 7.5 in men and 0.2 to 2.2 in women for every 100,000 persons per year [9]. Considering India’s population of ~ 1.4 billion, the actual numbers would be on the order of tens of thousands of new cases annually. What confounds this situation is the high ratio of mortality to incidence (0.95) and a reported median survival period of only 2–3 months, even with the best supportive care [10]. The reasons for this situation are several:

Patient Demographics and Causative Factors

There is a wide range for median age of liver cancer presentation, 40–70 years [9]. Apart from chronic HBV infection, several risk factors have been associated with HCC development, including HCV infection, alcoholism and exposure to fungal aflatoxin. Classically, 70–90% of HCC incidences have been seen with underlying liver cirrhosis, but the contribution of non-alcoholic fatty liver disease (NAFLD) independent of cirrhosis to HCC development is rising steeply. Increasingly prevalent chronic lifestyle conditions like obesity and diabetes mellitus, linked to NAFLD, are thus suspected to play a role in the malignant transformation of hepatocytes [11].

Symptomatology and Screening

HCC develops initially as slow growing nodules (with estimated doubling time of 1–19 months), which may be asymptomatic for years. Diagnosis based on external symptoms is challenging—gross symptoms such as pain, abdominal discomfort, weight loss, fatigue, decompensatory jaundice or ascites often manifest only when the disease is in an advanced stage with multiple hepatic nodules and occasionally extra-hepatic lesions [12]. For such patients many potentially curative treatments are not applicable, unless the disease is successfully downstaged.

Multiple scientific reports have urged a regular HCC screening program for high-risk groups to help in early identification and improved disease prognosis [13,14,15]. They have recommended screening at least for cirrhotic patients with HBV/HCV infections, but also admitted the difficulty of lack of consensus on non-cirrhotic patients at risk. Even in the target group, screening logistics are complicated given patient numbers, clarity of diagnosis and awareness of screening programs among patients and physicians. For less affluent countries like India, with significant portions of the population in rural/semi-urban areas, a screening program with adequate penetration and follow-up is a major endeavor for already burdened public healthcare systems. Kumar et al. have proposed a three-fold program for curbing HCC in India, consisting of (1) reducing exposure to carcinogenic hepatotoxins, (2) treating the chronic necro-inflammatory state of liver produced by hepatotoxins and (3) preventing recurrence after initial curative treatment [9]. This calls for a major commitment from the public health infrastructure with adequate consideration of logistics and economics.

Metastasis and Disease Recurrence

Due to delayed detection, HCC is curable in only a fraction of cases. HCC is mostly detected as a multi-focal phenomenon: Intra-hepatic metastases are common because of the spread of the primary lesions into the portal vein branches and the main portal vein; rarely, extra-hepatic metastases are observed in the lung or bone as well as porta-hepatic lymphadenopathy. Certain tumor foci may be missed, being undetectable by existing imaging techniques or a product of metastases that occurred prior to surgical intervention [90].

Unlike TACE, which requires release of the drug from the embolic matrix, SIRT radionuclides can exert cytotoxic action by beta-emission at the pre-capillary level bound within the matrix. Therefore, TARE agents can afford to be designed for greater stability with minimal leaching of radioactivity from the formulation. There are two categories of SIRT agents based on the type of embolic matrix: (1) radionuclide-tagged formulations of lipiodol and (2) radiolabeled microparticles.

Radionuclide-tagged Formulations of Lipiodol

In clinical trials nearly 3 decades ago, lipiodol was assessed for TARE after substitution labeling with iodine-131 (131I) [half-life 8 days, beta-energy (max) 0.6 meV, tissue penetration 0.6–2 mm], exhibiting good patient tolerance [91]. Long-term reports have shown up to 39 ± 8.3% OS at 3 years [92]. When applied in random selection trials as post-resection adjuvant therapy, it improved OS for up to 7 years (66.7% vs. 31.8% for control) [93]. Studies with [131I]lipiodol TARE found lower adverse effects than with TACE [94]. In India, [131I]lipiodol for TARE has been demonstrated capable of cost-effective indigenous preparation—using a semi-automated synthesis module and locally available reactor-produced radioisotope—of standard patient doses of 2.22 GBq 131I activity (as per European Association of Nuclear Medicine guidelines, corresponding to a mean liver dose of ~ 50 Gy) [95, 96]. This can be replicated in any radiopharmacy with the suitable setup and is an economical SIRT solution. [131I]lipiodol has certain disadvantages because of the radioisotope. Preparation must be done in a suitable ventilated cabinet to prevent accidental 131I aerosol release to ambient atmosphere. The 364-keV penetrative gamma emissions with the long 8 day half-life call for additional precautions in patient management. For example, it must be ensured that no individual in public receives > 5 mSv external dose from the patient. Hence, the patient may be discharged only after the dose at 1 m away reduces to 0.07 mSv/h [97], and necessary precautions must be followed in handling/disposal of their body waste [98]. Thyroid uptake of free 131I is also reported, though there is no consensus on the need for measures to protect against this [96]. Thus, while [131I]lipiodol has the advantage of being a well-known economical mode of TARE, it may not remain the first choice if other options become more widely available.

Lipiodol has also been prepared as a rhenium-188 (188Re) labeled formulation. Here, the transition metal forms stable lipophilic complexes with suitable ligands, such as AHDD (acetylated 4-hexadecyl-4,7-diaza-1,10-decanedithiol), DEDC (diethyl dithiocarbamate) and SSS [(S3CPh)2(S2CPh)], which can then be extracted into lipiodol. Unlike with 131I, no covalent bond exists between 188Re and lipiodol. With greater therapeutic energy and penetration (beta-energy max 2.1 meV, penetration range 2–10 mm), safer imaging-friendly gamma emission (155 keV) and a shorter half-life (16.9 h), 188Re is more suitable for TARE than 131I. Additionally, the ligands mentioned can form rhenium-188 complexes in much higher yield than the substitution labeling process for 131I and be extracted into lipiodol phase with moderate to high efficiency. Its availability through a versatile application “Good Manufacturing Practice” (GMP)-certified tungsten-188/rhenium-188 (188 W/188Re) radionuclide generator makes it convenient to elute rhenium-188 and prepare the radiopharmaceutical on demand in a radiopharmacy [99, 100]. Reports of 188Re-HDD in phase I and II trials indicate that escalation of administered radioactivity from 1.8–9.8 GBq showed good tolerance with minimal side effects, rapid renal clearance of blood radioactivity and regression/stabilization of the disease in an appreciable proportion of patients [101]. A multi-centric study by nuclear medicine departments in India and Vietnam found complete/partial disappearance of tumor or stable disease in > 68% of patients and survival rates of 58% at 24 months and 30% at 36 months, with a median survival of 980 days [99]. A more recent study showed the utility of 188Re-HDD/lipiodol for therapy in patients with solitary HCC not amenable to resection [102]. Moreover, post-administration SPECT imaging could be used to assess absorbed doses in target and normal tissue [103]. 188Re-HDD/lipiodol carries caveats of limited extraction (~ 60–70%) into lipiodol and adhesion to vial/syringe surfaces, making less therapeutic activity available for injection (50–60%) [103], but formulations like 188Re-DEDC/lipiodol and 188Re-SSS/lipiodol, capable of 80–90% extraction into lipiodol and lower surface adhesion tendencies, rectify this limitation. Phase I clinical studies with 188Re-labeled DEDC and SSS indicate good hepatic retention with minimal uptake in other tissues [104]. Automated synthesis modules for preparation of clinical scale doses of 188Re-lipiodol via DEDC and SSS have already been reported [105, 106]. In India, kits for formulating 188Re-lipiodol using DEDC have been indigenously developed, and preliminary clinical assessment at regional nuclear medicine centers has ascertained a favorable profile of the radiopharmaceutical [107]. The sole stumbling block to greater adoption of 188Re-lipiodol in India is the sparse local availability of 188W/188Re generators, still imported at a significant cost and subject to international market vagaries. An earlier report by Bal and Kumar strongly advocated the need for affordable 188Re generator technology [108], and the know-how for making various types of 188W/188Re generators in India using 188W raw material already exists [109, 110], but it would be a significant advantage for any future planned reactors to possess the requisite characteristics for indigenous 188W production for use in clinical-grade generators in India.

Radiolabeled Microparticles

Microparticles labeled with beta-emitters such as yttrium-90 (90Y) are the most widely employed form of SIRT for HCC. Made of degradation-resistant material with sufficiently large particle diameter (> 20 micron), they embolize in the terminal arterioles of tumor-feeding vasculature permanently, or at least long enough for the radiation dose to be deposited almost entirely [111]. 90Y is the most common radioisotope to address primary and secondary liver malignancies. Its 2.28-meV (maximum energy) pure beta emission, 11-mm maximum penetration range and 64.2-h half-life can provide an effective therapeutic dose to large and/or multi-nodal lesions [94]. Despite being tested for liver cancer therapy as early as 1982 [112], there are only few commercially available 90Y-labeled microparticle therapies for HCC: (1) 90Y-impregnated glass microspheres—Therasphere® (BTG, Canada); (2) 90Y-labeled resin microspheres—SIR-sphere® (Sirtex Medical, USA) [113]. The major differences between them are outlined in Table 1.

Table 1 Technical comparison of clinically available yttrium-90 labeled microspheres for trans-arterial radioembolization—Therasphere™ and SIR-Sphere® (data sourced from [91, 110])

Due to the greater radioactive concentration and higher specific gravity compared to SIR-Spheres® (3.2 g/cc vs. 1.6 g/cc), Therasphere® is less amenable to dose fractionation, which may be practiced for logistics in large-scale public healthcare facilities. The multi-fold higher particle count in SIR-spheres® also means higher embolism for a given radiation dose [114]. These aspects are expected to factor in when determining the specific eligibility criteria under which these agents may be prescribed.

As previously mentioned for imaging-based diagnosis, the administration of 90Y-labeled therapeutic microparticles is preceded 1–2 weeks by a safety scan using ~ 148-185 MBq of 99mTc-labeled MAA to simulate deposition of therapeutic microparticles in the vascular bed. This is primarily to determine the lung shunt fraction (LSF), the potential extent of shunting of these microparticles to the lung because of arteriovenous anastomoses in the tumor vasculature. This helps minimize the risk of radiation pneumonitis as an adverse effect. Existing literature recommends maximum lung exposure of 30 Gy in a single session and 50 Gy across multiple sessions, beyond which dose reduction is made or TARE is contraindicated [111, 114]. It may however be noted that some reports have raised doubts over the accuracy of LSF calculated from 99mTc-MAA scans [129]. SBRT and TARE/TACE have also helped to downstage multi-focal intermediate stage cancers to where they become eligible for resection/ablation or sustained patients during the waiting period for transplantation. The advantage of TARE over TACE in patients with concomitant PVT should be duly considered when preparing the treatment strategy in these cases. TARE and EBRT may be indicated in specific situations of post-resection adjuvant therapy where ablation is contraindicated. Multi-dose SBRT may prove useful in patients with single lesions where the location is not amenable to surgery and ablative measures might prove inadequate. A combination of TARE/TACE/SBRT with systemic chemotherapy can help patients with extra-hepatic metastases to downstage the disease to where it can be addressed with other tools. A critical potential application of radiotherapy is when HCC metastases infiltrate critical tissues like the brain [130]; most other modalities are of limited application here because of permeability/systemic toxicity issues and the potential danger of any invasive protocols. TARE (or any other approach) to treat the hepatic lesions may be paired with a targeted SBRT modality to specifically address the cranial metastases. Ready availability of specific techniques in terms of equipment and trained personnel at clinical centers is an important factor. In countries that have a significant HCC-afflicted population with limited public healthcare options, resective surgery, ablation, EBRT and selected embolic therapies (TARE/TACE) represent the major strategies available to patients. Since only a small proportion of HCC patients is at least initially eligible for resection, and ablative therapies are less useful for a significant proportion of diagnosed cases, there is a strong case to enhance clinical utilization of SBRT or TARE/TACE to manage or downstage the disease till other therapy options become viable. SBRT in combination with measures like chemotherapy would be useful in countries like China, which have many beam therapy centers for the population, and has also generated many clinical data on newer drugs and drug combinations effective against HCC. India with its limited access to HCC therapy-capable beam therapy centers may have to lean more on internalized radionuclide therapies. One obstacle toward this is the currently high cost of SIRT formulations that are imported. To address this, there should be greater clinical adoption of indigenously developed solutions that can provide similar benefits with easier availability and lower cost, some of which are discussed in the relevant sections of this report. Simultaneously, the infrastructure related to their production and on-site delivery should be enhanced to keep up with the perceived demand and eventually have the capability to export to other countries at more cost-effective rates as a worldwide public health initiative. For advanced multi-focal HCC cases, China’s advances in economically more favorable systemic chemotherapy can be adapted and followed by other nations with a large public healthcare burden. Similarly, depending on the proportion of patients with such needs, the technological means to deliver a targeted dose of EBRT for HCC or metastases in critical areas should also be made more widely available. Awareness in the clinical community regarding availability of these options for HCC is also essential in ensuring that appropriate patients receive the most optimal treatment/combination of treatments.

Conclusion

When viewed from a holistic perspective, the various approaches to treatment of liver cancer are revealed to complement each other when applied after judicious tailoring on the strength of an effective screening/diagnosis program to the individual patient’s requirements and careful monitoring of their impact to ensure optimal therapeutic benefit with minimal collateral damage. Radiation and radioisotope-based approaches are seen to be a necessary component of any holistic management protocol for HCC. What is required is strategic planning at both the level of the clinical institution and the level of national health policy to identify, promote and enhance availability of the specific approaches that can provide the best possible therapeutic benefit to the greatest proportion of patients that require it.