VEGFR Inhibitors for Uterine Metastatic Perivascular Epithelioid Tumors (PEComa) Resistant to mTOR Inhibitors. A Case Report and Review of Literature

Uterine perivascular epithelioid cell tumors (PEComas) are rare neoplasms. PI3K/AKT/mTOR pathway upregulation is critical for their pathogenesis and is often associated with TSC1/TSC2 inactivation. Although first line mTOR inhibitors are an effective treatment, metastatic PEComas eventually progress. A 53-year-old woman presented a 4-month history of post-menopausal vaginal bleeding. Clinical and radiological examination detected a uterine mass and a single S1 bone lesion. The patient underwent a radical hysterectomy and bone biopsy. The anatomopathological evaluation concluded to an oligo-metastatic uterine PEComa. The tumor harbored a heterozygous deletion of 9q34 that contains the TSC1 gene. Concerning the primary lesion, the resection was complete and the single bone metastasis was treated with radiotherapy. Three months later, the patient presented bone, lung and subcutaneous metastatic progression. An everolimus and denosumab treatment was initiated. After 2 years of treatment, a clinically significant bone, lung and subcutaneous progression was detected. Following a literature review of the possible therapeutic options, we initiated a second line treatment by pazopanib. This treatment resulted in regression of the subcutaneous lesions and stability of lung and bone metastases. In this challenging, rare setting, our report suggests single agent, anti-angiogenic, tyrosine kinase inhibitor to be effective as second line treatment of metastatic uterine PEComa progressing on mTOR inhibitors.


INTRODUCTION
Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal tumors, originating from the perivascular epithelioid cell-line (PEC) (1,2). PEComas are characterized by co-expression of melanocytic and myoid markers including actin, desmin, HMB-45, and Melan-A (3). S100 and CK are rarely expressed (4). The World Health Organization (WHO) defines PEComas as "mesenchymal tumors composed of histologically and immunohistochemically distinctive FIGURE 1 | Initial pathology. perivascular cells." PEComas is a relatively new subgroup of tumors, first described in 1992. Under the initial description, PEComas only included angiomyolipoma (AML) and clear cell "sugar" tumor of the lung (CCST). Currently, lymphangioleiomyomatosis (LAM) has also been added to the PEComa family (4,5). Although not all subsets of PEComas present malignant behavior, a considerable proportion exhibit malignant features including high proliferation rate and cytological atypia.
PEComas can occur at any age, but they are more common in the fourth decade. They affect more often women, which suggests a potential role of hormones in pathogenesis (6,7). PEComas have tropism for the retroperitoneum, the kidneys and the genitourinary tract, but rarely can affect other localizations. As far as uterine PEComas are concerned, they are usually located in the corpus. Rarely the uterine cervix can also be involved (1,5). The differential diagnosis of uterine PEComas is large and includes all types of uterine malignant and benign tumors. Especially challenging is their radiological distinction from smooth muscle tumors namely leiomyomas, a frequent benign tumor present in up to 80% of middle age women (8). PEComas can also be misdiagnosed for carcinomas, especially if visceral or cervical involvement is present, mimicking clear cell or other subtypes radiological characteristics.
The pathogenesis of PEComas is not yet fully understood. It has been hypothesized that these tumors are associated with tuberous sclerosis complex (TSC). This tumor-suppressor gene syndrome is caused by inactivation of TSC1 and TSC2, encoding hamartin and tuberin, respectively (9). These two proteins form a heterodimeric complex with inhibitor effect to the mammalian target of rapamycin (mTOR) activity. Inactivation of the tuberin/hamartin complex, results from a germline and /or loss-of-function mutation of either TSC1 or TSC2 genes. Subsequent permanent activation of mTOR promotes cell growth. Similar mutations have also been detected in sporadic, not associated with TSC, PEComas (10,11).
Many different angiogenesis inhibitors were reported effective for advanced PEComa treatment (4). Angiogenesis is a complex web of cytokines and receptors with intracellular and nuclear cascades for signal transmission. They are intimately related to tumor genesis, proliferation and invasion. Vascular endothelial growth factor (VEGF) over-expression is a prognostic factor, associated with increased risk of metastases and decreased overall survival, in patients with solid tumors. The VEGF receptors (VEGFR) are a family of tyrosine kinase (TK) receptors that include VEGFR-1, VEGFR-2, and VEGFR-3 expressed among tumor microenvironment stromal cells and endothelial cells. The platelet derived growth factor (PDGF) and its receptor (PDGFR) family includes PDGFR, c-Kit, and Flt-3. Their main effect is the proliferation and migration of cells.
The treatment of PEComas can be challenging, as there are no prospective trials nor established standard treatment guidance. Despite mTOR inhibitors, resistant or progressive diseases treatment is unclear. In this challenging context, where commonly used chemotherapies including anthracyclines, taxanes, and anti-metabolites have marginal or no effect, prospective research is urgently needed to determine second line treatment options (12). In our report, we present the efficacy of the 2nd line treatment by pazopanib, a multi-tyrosine kinase inhibitor, in a patient with a metastatic uterine PEComa, progressing after 2 years of everolimus treatment.

CASE REPORT
A 53 year-old woman presented a 4-month history of vaginal bleeding without associated abdominal pain or other symptoms. On the gynecological examination, a right side, para-uterine mass was detected. The vaginal ultrasound and MRI showed the 6 × 6 cm mass with no associated lymph node involvement. The PET-CT identified a single bone lesion in the sacral spine (S1). Tumor markers including CEA, CA125, CA19-9, and CA15-3 were within normal range.
The patient underwent radical hysterectomy and bone biopsy. Both bone biopsy and hysterectomy indicated an oligo-metastatic uterine PEComa, without cervical involvement, with high-grade nuclear features and lymphovascular invasions (Figure 1). The tumor expressed CD10, the myoid smooth muscle actin and HMB45. Focal anti-TFE3 was also observed (11,13). The single bone metastasis was treated with radiotherapy (5 fractions of 7 Gy for a total of 35 Gy).
Three months later, the patient presented asymptomatic bone, lung and subcutaneous recurrence. Targeted NGS (52cancer gene hotspot panel) detected no mutation but a heterozygous deletion of 9q34 that contains the TSC1 gene (Figure 2) (14), prompting a first line everolimus treatment (10 mg 1×/day, po) (15). For the bone metastasis, denosumab (120 mg 1/month sc) was initiated, and a quarterly followup by PET-CT as well as regular clinical surveillance was decided. On this treatment, the disease was controlled for 2 years, but unfortunately the patient started feeling pain in the subcutaneous lesion of the right thigh and clinical progression was noted. The PET-CT showed bone, lung and subcutaneous progression. A second line treatment by pazopanib and denosumab was introduced, based on reports on antiangiogenic tyrosine kinase inhibitors (TKIs) effect in PEComas (16, 17) ( Table 1).
During the treatment, the patient had regular clinical, biological and radiological controls. With the combination of pazopanib (800 mg 1×/day po) and denosumab, there was regression of the subcutaneous disease and stability of lung and bone metastasis for over a year Figure 3. It is important to note that all the treatments were well-tolerated, only with mild toxicities. No dose adaptation was necessary.

DISCUSSION
Both sporadic and TSC associated PEComas present mTOR pathway alterations. This provided the rational for rather successful use of mTOR inhibitors including sirolimus, everolimus or temsirolimus. Despite being a rare tumor with no specific randomized controlled trial assessing the optimal treatment sequence, mTOR inhibitors are currently considered the most effective treatment option for metastatic PEComas (25)(26)(27)(28)(29). In the case of our patient, single agent everolimus treatment at the standard dose of 10 mg per day was effective for up to 2 years Albeit this observation, it should be noted that in the reported cases the response rate and PFS varies, with a PFS of 9 months (4), according to the clinical context and previous prescribed treatments.
At the time of symptomatic progression, the therapeutic plan of our patient became even more challenging. Since no targetable alteration was detected in the 52-genes tumor DNA sequencing, we underwent a literature review on Scopus and PubMed. The key word used were "metastatic" and "PEComa, " "uterine perivascular epithelioid cell tumor, " "soft tissue sarcomas, " "mTOR, " "treatment." We selected publications from 2000 to 2019.
The review pointed out potential benefit from anti-angiogenic treatment as an effective therapeutic option for our patient (16, 17). Furthermore, the local funding system enables pazopanib treatment for soft tissue sarcomas.
Pazopanib is an oral, multi-targeted tyrosine kinase inhibitor, which has activity against VEGF-1-3, PDGFRαβ and KIT, resulting in tumor growth blockage and angiogenesis inhibition. The Phase III, placebo-controlled, double-blind PALETTE trial, comparing the efficacy of pazopanib vs. placebo in patients with non-adipocytic soft tissue sarcoma already treated with doxorubicin, showed a significant increase in PFS with pazopanib (4.6 vs. 1.6 months; P < 0.001); ORR was 6%. Median OS was 12.5 months with pazopanib vs. 10.7 months with placebo, but was not statistically significant (HR: 0.86, 95% CI: 0.67-1.11; p = 0.25). There is no precision on whether patients with PEComas were included in the trial (16). The SPIRE trial showed the activity of pazopanib in patients with soft tissue sarcomas, based on reports on specific histological subtypes (17). Two of the patients included in the trial were diagnosed with PEComas.
Sunitinib and regorafenib are approved for gastrointestinal stromal tumor (GIST), but not for other STS, as the clinical trials of these agents as STS treatment are limited to single-arm phase II trials (30,31).   Sorafenib is another multi-TKI that has only showed limited activity in a phase II trial (32) including patients with six different types of STS. There was no precision on whether patients with PEComas were included.
In our review three interesting therapeutic combinations were included. One case-report reported the combination of sorafenib with sirolimus as effective palliative therapy in malignant PEComa (33). In another report bevacizumab, a monoclonal antibody (MoAb) targeting VEGF was evaluated. The combination of bevacizumab with doxorubicin was evaluated in a phase II trial, among 17 patients with metastatic, anthracycline-naïve, soft tissue sarcomas (34). The overall response rate was 12%, equal to the observed for single-agent doxorubicin arm. However, stable disease, lasting four cycles or longer, was observed in 65% of patients. Interestingly, in a retrospective case series published in 2018, seven patients with advanced PEComa progressing on mTOR inhibitor (sirolimus) were treated with exemestane, an aromatase inhibitor, in combination with everolimus. Authors reported restoration of tumors to mTOR inhibitor leading to a median PFS of 7 months and median duration of the response 11 months (35).
Although with limited impact and no comparison arm, our treatment decision lead to a 12 months stabilization of our patient lung and bone disease and notably with regression of her symptomatic subcutaneous metastasis.

CONCLUSION
PEComas are rare mesenchymal neoplasms, for which there is no systemic treatment established. Our report provides data that mTOR inhibitors and anti-angiogenic TKI can be effective treatments, with an acceptable toxicity profile. Further research is needed in order establish the optimal treatment sequence in this setting.