Pigmented villonodular synovitis

Current Systemic Treatment Options for Tenosynovial Giant Cell Tumor/Pigmented Villonodular Synovitis: Targeting the CSF1/CSF1R Axis

OPINION STATEMENT

Adequate surgical resection remains the treatment of choice for tenosyovial giant cell tumor (TGCT). However, diffuse type TGCT (D-TGCT) is more difficult to resect and has a higher rate of recurrence (up to 50 %), which is often multiple. D-TGCT is rarely lethal and only rare cases of metastases have been described. Nevertheless, patients might have a significant decline in their quality of life due to multiple operations, which may sometimes result in a partial loss of function of the affected joint and may also be associated with perioperative morbidity and secondary arthrosis. As of today, no systemic treatment is approved for this rare disease. The aims of systemic therapy in the context of a non-lethal tumor are to reduce surgical morbidity and to preserve function and patient quality of life. Because TGCT is associated with characteristic cytogenetic abnormalities resulting in the overexpression of CSF1, systemic therapies targeting the CSF1/CSF1R axis (imatinib, nilotinib, emactuzumab, and PLX3397) have been tested in patients with locally advanced or relapsed D-TGCT. The more recent and more specific CSF1R inhibitors have shown a very interesting clinical activity with acceptable toxicity in early phase trials. These results will need to be confirmed in larger, ideally randomized, trials. But the high rate of clinical and functional improvement seen in some patients with advanced D-TGCT, often after multiple operations, suggests that these inhibitors will likely have a role in the management of patients with an inoperable disease; the definition of "inoperable TGCT" still requires refinement to reach a consensus. Another point that will need to be addressed is that of "the optimal duration of therapy" for these patients. Indeed, we and others have observed often prolonged clinical benefit and symptomatic relief even after treatment was stopped, with both monoclonal antibodies and tyrosine kinase inhibitors. Responses were observed very early on with emactuzumab and PLX3397, and patients experienced significant symptom improvement within a few weeks of starting therapy (2-4 weeks). Another possible application of CSF1R inhibitors could be used either as a preoperative or postoperative therapy for patients with operable TGCT. However, we currently lack sufficient follow-up to adequately address these questions which will each require specific trial designs. Overall, the striking clinical activity of CSF1R specific inhibitors in TGCT has created great enthusiasm among clinicians, and further development of these agents is clearly medically needed. Nevertheless, further investigations are necessary to validate those treatments and assess how to best incorporate them among other treatment modalities into the overall therapeutic strategy for a given patient.

CSF1R inhibition with emactuzumab in locally advanced diffuse-type tenosynovial giant cell tumours of the soft tissue: a dose-escalation and dose-expansion phase 1 study

BACKGROUND

Diffuse-type tenosynovial giant cell tumour (dt-GCT) of the soft tissue (alternatively known as pigmented villonodular synovitis), an orphan disease with unmet medical need, is characterised by an overexpression of colony-stimulating factor 1 (CSF1), and is usually caused by a chromosomal translocation involving CSF1. CSF1 receptor (CSF1R) activation leads to the recruitment of CSF1R-expressing cells of the mononuclear phagocyte lineage that constitute the tumor mass in dt-GCT. Emactuzumab (RG7155) is a novel monoclonal antibody that inhibits CSF1R activation. We have assessed the safety, tolerability and activity of emactuzumab in patients with Dt-GCT of the soft tissue.

METHODS

In this phase 1, first-in-human dose-escalation and dose-expansion study, eligible patients were aged 18 years or older with dt-GCT of the soft tissue with locally advanced disease or resectable tumours requiring extensive surgery, an Eastern Cooperative Oncology Group performance status of 1 or less, measurable disease according to Response Evaluation Criteria In Solid Tumors version 1.1, and adequate end-organ function. Patients with GCT of the bone were not eligible. Patients received intravenous emactuzumab at 900 mg, 1350 mg, or 2000 mg every 2 weeks in the dose-escalation phase and at the optimal biological dose in a dose-expansion phase. The primary objective was to evaluate the safety and tolerability of emactuzumab, and to determine the maximum tolerated dose or optimal biological dose. All treated patients were included in the analyses. Expansion cohorts are currently ongoing. This study is registered with ClinicalTrials.gov, number NCT01494688.

FINDINGS

Between July 26, 2012, and Oct 21, 2013, 12 patients were enrolled in the dose-escalation phase. No dose-limiting toxicities were noted in the dose-escalation cohort; on the basis of pharmacokinetic, pharmacodynamic, and safety information, we chose a dose of 1000 mg every 2 week for the dose-expansion cohort, into which 17 patients were enrolled. Owing to different cutoff dates for safety and efficacy readouts, the safety population comprised 25 patients. Common adverse events after emactuzumab treatment were facial oedema (16 [64%] of 25 patients), asthenia (14 [56%]), and pruritus (14 [56%]). Five serious adverse events (periorbital oedema, lupus erythematosus [occurring twice], erythema, and dermohypodermitis all experienced by one [4%] patient each) were reported in five patients. Three of the five serious adverse events-periorbital oedema (one [4%]), lupus erythematosus (one [4%]), and dermohypodermitis (one [4%])-were assessed as grade 3. Two other grade 3 events were reported: mucositis (one [4%]) and fatigue (one [4%]). 24 (86%) of 28 patients achieved an objective response; two (7%) patients achieved a complete response.

INTERPRETATION

Further study of dt-GCT is warranted and different possibilities, such as an international collaboration with cooperative groups to assure appropriate recruitment in this rare disease, are currently being assessed.

FUNDING

F Hoffmann-La Roche.