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large pediatric tumor study groups. The current treatment approach of pediatric liver tumors is perhaps
best exemplified with the treatment algorithm of hepatoblastoma [23,24] , the most common pediatric liver
tumor [21,22] . Hepatoblastoma typically arises before or right around 3 years of age [25,26] . Hepatoblastoma
shares this important feature with essentially all other pediatric liver tumors, with the exception of HCC
of childhood [21,22] . While the latter is found mostly in adolescence, the large majority of all other childhood
tumors arise at very young age. As it is easily understandable, this insight has significant impact when
selecting the operative approach.

Traditionally, knowledge regarding hepatoblastoma has been extracted from the four major cooperative
study groups: the International Childhood Liver Tumors Strategy Group (SIOPEL), Children’s Oncology
Group (COG), the German Society for Pediatric Oncology and Hematology, and the Japanese Study Group
for Pediatric Liver Tumors. Because the numbers of patients in these individual groups were low due to
the rarity of the disease and all groups used fundamentally different staging and stratification systems, the
comparability of the data obtained was limited [23,24] . For this reason, with the involvement of the four groups,
a worldwide coalition for the study of hepatoblastomas was formed [4,24] . As one of its first tasks, CHIC has
recently generated a novel risk stratification based on data from more than 1,600 children treated for 25
years for hepatoblastoma. This risk stratification is based on the stage classification according to PRETEXT
(pre-treatment extension), the initial AFP value at diagnosis, the presence of metastases, the presence of
vascular invasión and the age of the child, and characterizes the four risk levels: very low, low, intermediate
[24]
and high . Because this stratification system will be used in a new global research study on hepatoblastoma
(PHITT) starting in 2018, all other risk stratifications regarding hepatoblastoma have become obsolete. In
the PHITT trial, the PRETEXT (pre-treatment extension) grouping system of SIOPEL is used for childhood
[27]
liver tumors . This system is based exclusively on pretherapeutic imaging and is thus independent of the
surgical or therapeutic intervention. It describes the extent of the tumor across the 4 surgical sectors of the
liver and additionally contains defined PRETEXT risk factors. PRETEXT risk factors include invasion of the
tumor into one or more hepatic veins (abbreviated by the letter V) or portal vein (P) and extrahepatic tumor
invasion (E), tumor rupture (R) or multifocality of the tumor (F). Because a high prognostic relevance for
[24]
this classification has been proven, it has gained international acceptance . In the studies of the US COG,
until recently, the traditional staging system, which relies on tumor size in terms of resectability, was used
at the same time [21,22] . Because of its primarily surgical perspective, this system has above all relevance in
[24]
[21]
HCC . However, the COG-staging system is not part of the PHITT trial .
Since most childhood liver tumors are either benign and partly regress spontaneously (infantile hepatic
hemangioma) or respond well to chemotherapy (hepatoblastoma), primary resection is usually not indicated
as a primary therapeutic approach [21,22] . This understanding is especially true in infants, toddlers and
schoolchildren. Primary resection in benign tumors is indicated when they grow in size, when there are
[22]
radiological changes suspicious of malignancy and/or if they become symptomatic . As part of the PHITT
trial, the surgical treatment decision is clearly regulated and represents a separate study branch within the
trial. According to the trial, an initial resection is indicated in children only if there is a stage PRETEXT I or
II liver tumor and the tumor is safely removable via a simple lobectomy (trial details at https://clinicaltrials.
gov/ct2/show/NCT03017326). All other children undergo a biopsy first and then, if the diagnosis of a
hepatoblastoma is confirmed, two cycles of chemotherapy are initiated. After reimaging, the resection will
be performed as long as it can be carried out as a simple lobectomy and only if the tumor can be removed
safely and completely with this approach. If this is not possible, there will be two more chemotherapy blocks,
blocks 3 and 4. During the administration of blocks 3 and 4, the child is evaluated for liver transplantation,
which can then be carried out without further delay after completion of block 4. In individual cases, the
improvement after the end of block 4 may instead of the liver transplantation call for a complex or extended
resection, always on the premise that the tumor can be completely removed. In cases where there is doubt
of resectability, the surgery can be performed when an organ becomes available and with another recipient