Therapeutic benefit of larotrectinib over the historical standard of care in patients with locally advanced or metastatic infantile fibrosarcoma (EPI VITRAKVI study)

BACKGROUND

Patients with infantile fibrosarcoma (IFS) have shown strong and long-lasting responses to larotrectinib, a tropomyosin receptor kinase inhibitor (TRKi), in single-arm clinical trials. Conventional chemotherapy has also shown important efficacy. But, until now, no comparative data exist. This study aims to assess the therapeutic benefit of larotrectinib over the current standard of care (SOC) of chemotherapy in paediatric patients with locally advanced or metastatic IFS.

PATIENTS AND METHODS

EPI VITRAKVI is a retrospective, observational, externally controlled study (NCT05236257). Data of patients aged ≤21 years with locally advanced or metastatic IFS treated with larotrectinib in the phase I/II SCOUT trial (NCT02637687) were compared with those of an external historical control group (data of Institut Curie and Cooperative Weichteilsarkom Studiengruppe) treated with a chemotherapy-based regimen. Between-group differences were assessed after balancing groups using inverse probability of treatment weighting (IPTW).

RESULTS

In total, 93 patients were compared, 51 in the larotrectinib arm and 42 in the external control arm. After therapy, 4 patients (7.8%) in the larotrectinib group had a medical treatment failure event [start of new systemic treatment (2 cases), mutilating surgery (2 cases)] versus 15 (35.7%) in the external control group [start of new systemic treatment (6 cases), mutilating surgery (5 cases), radiation therapy (2 cases), and death (2 cases)]. Larotrectinib was associated with an 80% reduced likelihood of encountering a medical treatment failure event, when compared to the external control group (weighted and stratified hazard ratio 0.20, 95% confidence interval 0.06-0.63, P = 0.0060). These results were confirmed by sensitivity analyses, including exact matching, and subgroup analyses for number of lines of treatment.

CONCLUSIONS

Treatment with larotrectinib reduced the need of subsequent therapies compared to SOC with chemotherapy in children with locally advanced or metastatic IFS, regardless of the line of treatment.

[Epithelial childhood liver tumors : An overview of the new WHO classification for pediatric tumors]

Pediatric liver tumors are very rare tumors and account for less than 1% of all childhood malignancies. By far the most common tumors are hepatoblastomas. This review discusses epithelial malignant childhood liver tumors, with particular attention to the morphology of the different hepatoblastoma subtypes. In addition, other malignant liver tumors such as the so-called hepatocellular tumor NOS and the second-most common childhood liver tumor, the hepatocellular carcinoma, are discussed. In addition to the typical morphological characteristics, the immunohistochemical and molecular aspects are also be presented, which can help to distinguish these entities with often overlapping morphology.

Rapid, complete and sustained tumour response to the TRK inhibitor larotrectinib in an infant with recurrent, chemotherapy-refractory infantile fibrosarcoma carrying the characteristic ETV6-NTRK3 gene fusion

BACKGROUND

The ETV6-NTRK3 gene fusion is present in the majority of cases of infantile fibrosarcoma (IFS) and acts as a potent oncogenic driver. We report the very rapid, complete, and sustained response of an advanced, chemotherapy-refractory, recurrent IFS to targeted treatment with the oral tropomyosin receptor kinase (TRK) inhibitor larotrectinib.

PATIENT AND METHODS

A male infant born with a large congenital IFS of the tongue had the tumour surgically resected at age 4 days. Within 2 months, he developed extensive lymph node recurrence that progressed during two cycles of vincristine-doxorubicin-cyclophosphamide chemotherapy. At screening, a large right cervical mass was clinically visible. Magnetic resonance imaging (MRI) revealed bilateral cervical and axillary lymph node involvement as well as infiltration of the floor of the mouth. The largest lesion measured 5.5×4.5×4.4 cm (ca. 55 cm3). The patient started outpatient oral larotrectinib at 20 mg/kg twice daily at age 3.5 months.

RESULTS

After 4 days on treatment, the parents noted that the index tumour was visibly smaller and softer. The rapid tumour regression continued over the following weeks. On day 56 of treatment, the first scheduled control MRI showed the target lesion had shrunk to 1.2×1.2×0.8 cm (ca. 0.6 cm3), corresponding to a complete response according to the Response Evaluation Criteria In Solid Tumors version 1.1. This response was maintained over subsequent follow-up visits, and on day 112 at the second control MRI the target lymph node was completely normal. At last follow-up, the disease remained in complete remission after 16 months on larotrectinib, with negligible toxicity and no safety concerns.

CONCLUSION(S)

Selective TRK inhibition by larotrectinib offers a novel, highly specific and highly effective therapeutic option for IFS carrying the characteristic ETV6-NTRK3 gene fusion. Its use should be considered when surgery is not feasible. (NCT02637687).

[Rare childhood kidney tumors]

Pediatric kidney tumors are rare and account for about 6% of all childhood malignancies. By far the most common tumors are nephroblastomas. This review presents rare childhood renal tumors. Mesoblastic nephroma, as tumors of the low risk group, as well as the clear-cell sarcomas of the kidney and malignant rhabdoid tumors, as tumors of the high-risk group, and the so-called anaplastic sarcomas of the kidney will be discussed.Due to the significantly divergent therapy, a correct diagnosis is important. Due to the often overlapping morphology, pathologic diagnosis is often difficult. In addition to the typical morphologic features, the specific immunohistochemical aspects as well as the known molecular changes will be presented.

[Pediatric tumors with spindle cell morphology]

Spindle cell tumors in childhood are rare lesions with a heterogeneous morphological picture and clinical course, ranging from benign lesions to fully malignant tumors. The clinical assessment of these tumors is often challenging since some of them show fast growth dynamics but are utterly benign, while a subset of slow-growing tumors can represent malignant entities. Due to the rarity of these tumors as well as the overlapping morphology and the often uncharacteristic immunohistochemical profiles, the pathologic diagnosis is often also difficult. This review gives an overview of some of the more common pediatric spindle cell tumors. In addition to the morphological features and immunohistochemical aspects, specific molecular changes are discussed. Here, some of the newly described translocations that may imply therapeutic options, are presented.