Niklas Pal

Intratumoral genome diversity parallels progression and predicts outcome in pediatric cancer

Genetic differences among neoplastic cells within the same tumour have been proposed to drive cancer progression and treatment failure. Whether data on intratumoral diversity can be used to predict clinical outcome remains unclear. We here address this issue by quantifying genetic intratumoral diversity in a set of chemotherapy-treated childhood tumours. By analysis of multiple tumour samples from seven patients we demonstrate intratumoral diversity in all patients analysed after chemotherapy, typically presenting as multiple clones within a single millimetre-sized tumour sample (microdiversity). We show that microdiversity often acts as the foundation for further genome evolution in metastases. In addition, we find that microdiversity predicts poor cancer-specific survival (60%; P=0.009), independent of other risk factors, in a cohort of 44 patients with chemotherapy-treated childhood kidney cancer. Survival was 100% for patients lacking microdiversity. Thus, intratumoral genetic diversity is common in childhood cancers after chemotherapy and may be an important factor behind treatment failure.

A 10-year experience of outcome in chemotherapy-treated hereditary retinoblastoma

The aim is to report the 10‐year retrospective experience of systemic chemotherapy for a population‐based group of patients with hereditary retinoblastoma at a national referral centre. The outcomes include control rates, treatment side‐effects, adjuvant therapy, failure rate, survival, secondary cancers and visual acuity.

Birth characteristics and Wilms tumors in children in the Nordic countries: A register‐based case–control study

Little is known about causes of Wilms tumor. Because of the young age at diagnosis, several studies have looked at various birth characteristics. We conducted a registry‐based case–control study involving 690 cases of Wilms tumor aged 0–14 years, occurring in Denmark, Finland, Norway or Sweden during 1985–2006, individually matched to five controls drawn randomly from the Nordic childhood population. Information on birth characteristics was obtained from the population‐based medical birth registries. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) using conditional logistic regression analysis. We observed a distinct association between Wilms tumor and high birth weight (≥4 kg) for girls (OR 1.97, CI 1.50–2.59) but not for boys (1.04, 0.78–1.38); overall, the OR was 1.43 (1.17–1.74). Among girls, risk increased by 28% (15–42%) per 500 g increase in birth weight. Large‐for‐gestational age girls also had a higher risk (2.48, 1.51–4.05), whereas no effect was seen for boys (1.12, 0.60–2.07). An association was seen with Apgar score at 5 min < 7 for both sexes combined (5.13, 2.55–10.3). ORs close to unity were seen for parental age and birth order. In our large‐scale, registry‐based study, we confirmed earlier observations of an association between high birth weight and risk of Wilms tumor, but we found an effect only in girls. The higher risk of infants with low Apgar score might reflect hypoxia causing cell damage, adverse side effects of neonatal treatment or reverse causation as low Apgar score might indicate the presence of a tumor.

Incidence and survival analyses in children with solid tumours diagnosed in Sweden between 1983 and 2007

Aim:  Solid tumours constitute 40% of childhood malignancies. The Swedish Childhood Cancer Registry is population based and includes all children with cancer reported from the six paediatric oncology centres in Sweden. The aim was to investigate incidence and survival.

Malignant ectomesenchymoma in children and adolescents: Report from the Cooperative Weichteilsarkom Studiengruppe (CWS)

Malignant ectomesenchymoma (MEM) is a soft tissue tumor with heterologous rhabdomyoblastic components believed to arise from pluripotent migratory neural crest cells. To date merely 50 cases have been published and the knowledge about the course of disease and optimal treatment is limited.

Confined trisomy 8 mosaicism of meiotic origin: A rare cause of aneuploidy in childhood cancer

Whether chromosome abnormalities observed in tumor cells may in some cases reflect low‐grade somatic mosaicism for anomalies present already at zygote formation, rather than acquired somatic mutations, has for long remained a speculation. We here report a patient with Wilms tumor, where constitutional somatic mosaicism of trisomy 8 was detected in a previously healthy 2 ½‐year‐old boy. Single Nucleotide Polymorphism (SNP) array analysis of tumor tissue revealed a complex distribution of allele frequencies for chromosome 8 that could not be explained solely by mitotic events. Combined analysis of allele frequencies, chromosome banding, and fluorescence in situ hybridization revealed that the majority of tumor cells contained four copies of chromosome 8, with three distinct haplotypes at a 2:1:1 ratio. Because the patient had not been subject to organ transplantation, these findings indicated that the tumor karyotype evolved from a cell with trisomy 8 of meiotic origin, with subsequent somatic gain of one additional chromosome copy. Haplotype analysis was consistent with trisomy 8 through nondisjunction at meiosis I. Matched normal renal tissue or peripheral blood did not contain detectable amounts of cells with trisomy 8, consistent with the complete lack of mosaic trisomy 8 syndrome features in the patient. This case provides proof of principle for the hypothesis that tumor genotypes may in rare cases reflect meiotic rather than mitotic events, also in patients lacking syndromic features.

Convergent evolution of 11p allelic loss in multifocal Wilms tumors arising in WT1 mutation carriers

Wilms tumors in patients with constitutional WT1 mutations are examples of Knudsons tumor suppressor paradigm, with somatic inactivation of the second allele occurring through 11p loss of heterozygosity. The time point of this second hit has remained unknown. We analyzed seven Wilms tumors from two patients with constitutional WT1 mutations by whole exome sequencing and genomic array. All tumors exhibited wild type WT1 loss through uniparental isodisomy. Each tumor had a unique genomic breakpoint in 11p, typically accompanied by a private activating mutation of CTNNB1. Hence, convergent evolution rather than field carcinogenesis underlies multifocal tumors in WT1 mutation carriers.

Four evolutionary trajectories underlie genetic intratumoral variation in childhood cancer

A major challenge to personalized oncology is that driver mutations vary among cancer cells inhabiting the same tumor. Whether this reflects principally disparate patterns of Darwinian evolution in different tumor regions has remained unexplored1–5. We mapped the prevalence of genetically distinct clones over 250 regions in 54 childhood cancers. This showed that primary tumors can simultaneously follow up to four evolutionary trajectories over different anatomic areas. The most common pattern consists of subclones with very few mutations confined to a single tumor region. The second most common is a stable coexistence, over vast areas, of clones characterized by changes in chromosome numbers. This is contrasted by a third, less frequent, pattern where a clone with driver mutations or structural chromosome rearrangements emerges through a clonal sweep to dominate an anatomical region. The fourth and rarest pattern is the local emergence of a myriad of clones with TP53 inactivation. Death from disease was limited to tumors exhibiting the two last, most dynamic patterns.Multiregional analysis in 54 childhood cancers highlights four evolutionary patterns of intratumoral variation. Multiple patterns are often found in the same tumor, suggesting that tumors follow different evolutionary strategies concurrently.

Intra-arterial chemotherapy for retinoblastoma in Sweden - evaluation of treatment efficacy and complications

Editor, O ver the last 20 years, delivery of chemotherapy selectively to the ophthalmic artery in the management of retinoblastoma has been developed and reported as highly successful, by a few large specialized centres in Japan and North America (Gobin et al. 2011; Suzuki et al. 2011; Shields et al. 2014). Today, the evidence for intra-arterial chemotherapy (IACT) is based on a large number of publications presenting data from a small number of large patient cohorts treated at the aforementioned centres (Yousef et al. 2016). With high success rates in avoiding enucleation combined with a relatively low complication rate, IACT is now considered as first-line standard care at these centres, and in 2011, IACT had been performed at tertiary referral hospitals in 26 highand middleincome countries (Gobin et al. 2011). Despite the broad implementation of IACT in recent years, with the awareness of the lack of high-level evidence, no prospective multicentre clinical trial on IACT has yet been presented and there are uncertainties regarding the outcomes when IACT is introduced at and performed by clinical centres below a critical patient volume (Yousef et al. 2016). Retinoblastoma is diagnosed in six to eight children in Sweden yearly (Seregard et al. 2004; Bartuma et al. 2014). Prior to 2012, primary treatment in Sweden for children with uniand bilateral small tumours with potential salvage of vision consisted of systemic chemotherapy in combination with focal therapies, such as brachytherapy, transpupillary thermotherapy, laser photocoagulation or fractionated external radiotherapy (Seregard et al. 2004; Bartuma et al. 2014). Enucleation served as the single treatment option for large tumours and in advanced retinoblastoma failing primary treatment (Seregard et al. 2004; Bartuma et al. 2014). The Karolinska University Hospital in collaborationwith St Erik EyeHospital introduced IACT for retinoblastoma in Sweden 2012. The neurointerventional unit at Karolinska serves as a tertiary referral centre for treatment of a wide array of neurovascular diseases. We report our experience introducing IACT to retinoblastoma patients from the relatively small population of Sweden to provide clinicians in centres with similar conditions an estimate of success rates and treatment complications (Table 1). Thirteen patients with intraocular retinoblastoma received IACT with melphalan between 2012 and 2015 in Sweden. The outcome measures were globe salvage and treatment complications. A total number of 39 attempts of IACT were performed in 13 patients and 13 eyes. Two patients were excluded due to aberrant vascular anatomy. Melphalan delivery was successful in 30 procedures (77%). Globe salvage was achieved in eight of 11 eyes (73%). A total of 33 adverse events were observed in 13 patients. The most common event was nausea post-treatment (31%). Three adverse events required medical intervention and/or hospitalization. Cerebral embolization was detected angiographically in two patients without evidence of neurological deficit or ischaemic injury at clinical examination and follow-up magnetic resonance imaging (MRI). In conclusion, we report globe salvage rates and complications comparable to rates presented in a recent systematic review, although we did not reach the outstanding injection success rates reported by internationally leading centres. We encountered the previously unreported complication of procedure-related cerebral embolism. Although not leading to detectable ischaemic injury, we feel that this finding is an important contribution in the ongoing worldwide documentation of this technique.

Incidence and Survival Analyses in Children with Solid Tumours Diagnosed in Sweden 1983-2007.

Aim:  Solid tumours constitute 40% of childhood malignancies. The Swedish Childhood Cancer Registry is population based and includes all children with cancer reported from the six paediatric oncology centres in Sweden. The aim was to investigate incidence and survival.