Challenges in Diagnosing Metastatic Uterine PEComa: Insights from Two Case Studies

Introduction

In 1992, the “Perivascular Epithelioid Cells” concept was first described by Bonetti et al, and in 1996 Zamboni et al first used the term “PEComa” to describe the uncommon mesenchymal tumors made up of these cells [1–4]. In 2002, the World Health Organization (WHO) recognized this new class of tumor named “mesenchymal tumors composed of histologically and immunohistochemically distinctive perivascular epithelioid cells” [1,3–5]. In 2020, the WHO designated several categories of PEComa: angioleiomyoma (kidney), lymphangioleiomyomatosis, clear cell “sugar” tumor of the lung (CCST), clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres (CCMT), and non-specific types of PEComa from soft tissues, bone, and viscera (PEComa-not otherwise specified) [5]. These very rare tumors are usually present in young to middle-aged adults and occur more frequently in females, with a male-to-female ratio of 1: 5 [6].

Microscopically, this tumor is characterized by a perivascular distribution of epithelioid cells constituted by a clear or granular eosinophilic cytoplasm with inconstant pleomorphism and stromal hyalinization [4,7,8].

PEComas are involved in the reproductive system in 25% of the female population: the uterus is involved in about 75% of cases [2,6,7,9–11]. The other reproductive system sites are the cervix (10%), vagina (3%), ovaries (2%), broad ligaments (2%), and round ligaments (1%) [6]. Metastases are found in 15% of cases, usually to the lymph nodes [6].

Complete cytoreductive surgery is the most commonly recommended primary treatment, with adjuvant therapy, such as mTOR inhibitor, or, less frequently, radiotherapy, if the tumor is considered high-risk [2].

We report 2 cases of advanced malignant uterine perivascular epithelioid cell tumor (PEComa) diagnosed in a 74-year-old woman and a 50-year-old woman. They both underwent cytoreductive surgery in our center, with an adjuvant targeted therapy administered to the second woman.

Case Reports

CASE 1:

A 74-year-old White woman was admitted to our hospital’s Emergency Department for deterioration of general condition for 15 days. She reported having abdominal pain, diarrhea, asthenia, and inappetence with loss of 20 kg in 3 months. She also had insulin-dependent diabetes, asthma, scoliosis, and a thyroid goiter, and had undergone 2 C-sections, an appendectomy, and hernia repair. On clinical examination, the abdomen was tender and bloated by a bulky palpable mass. The blood sample showed an inflammation with 13 040 white blood cells/mm³ and C-reactive protein (CRP) at 215 mg/L.

A computed tomography (CT) scan (Figure 1) revealed an abdominal mass, with necrotic center, measuring 190×190×110 mm. The epicenter of the tumor lesion seemed to correspond to the mesentery. The uterus was heterogeneous and there were some nodular formations at the peritoneum of the pouch of Douglas, without ascites, signaling peritoneal carcinomatosis. We also found a 12-mm suspected solid hepatic focal lesion in segment IV.

Magnetic resonance imaging (MRI) detailed the characteristics of the uterus (Figure 2) and the mesenteric mass (Figure 3). The uterus was anteverted and anteflexed and measured 40×30×36 mm. We noted a hypersignal lesion on T2-weighted imaging in the endometrium infiltrating the myometrium over the entire thickness, with deformation of the uterine serosa. This lesion was positive in diffusion and took the contrast heterogeneously. Moreover, we observed a lateralized submesocolic abdominal mass on the right, of very heterogeneous signal, measuring 180 mm of transverse diameter, with positive diffusion taking the contrast. The mass was most likely of adnexal origin, possibly corresponding to a secondary lesion or a primary uterine lesion. The left ovary was no longer individualized. We noted the presence of nodular lesions in abdominal fat, suggesting implants of carcinosis. The CT thorax and the scintigraphy were negative.

A biopsy sampled by exploratory laparoscopy revealed foci of necrosis with cell proliferation made up of an eosinophilic cytoplasm.

We chose the surgical option during our multidisciplinary council; the procedure consisted of resection of the bulky submesocolic mass (Figure 4) and 70 cm of the small intestine, which presented many serous nodules. The tumor mass measured 210×160×100 mm, weighed 1425 g, and presented a lobular aspect, with a well-delineated necrotic lesion occupying one-third of the specimen. Other samples were sent separately: they formed a cluster of 180×100×50 mm after aggregation.

As demonstrated in the biopsy, the microscopic examination revealed coagulative necrosis ranges accompanied by a proliferation of large, polymorphic-appearing, closely associated cells with round nuclei, often with a hyperchromatic prominent nucleolus with mild to moderate pleomorphism with mitotic count 7 mitoses per 10 high-power fields (HPF). These fusi-form epithelioid cells had a cytoplasm with a frosted glass appearance, high eosinophilic color, and some hyaline micronodules. Cells in the lesion (Figure 5) formed a diffuse range and a fascicular architecture.

The immunohistochemistry of the surgical specimen (Figure 6) was partially positive for HMB-45 (especially around foci of necrosis) and for Melan-A. Caldesmon, actin, and desmin were diffusely expressed. Vimentin and TP53 were mildly expressed. Estrogen receptors and progestin receptors were both 8/8. WT was positive, but BerEP4, calretinin, protein S100, inhibin, cytokeratin 7-19-20, CD117, glypican, and arginase were all negative.

Unfortunately, the immediate post-operative period was marked by asthenia and severe inflammation. The patient died 2 months after the surgery in palliative care without receiving any systemic targeted therapy.

CASE 2:

Our second patient was 50-year-old woman originally from North Africa. She had consulted her gynecologist for menorrhagia and pelvic pain. Her medical history was obesity (body mass index: 34 kg/m²), high blood pressure, hypothyroidism, atrial fibrillation, and Leiden factor V mutation. Her surgical history included inguinal hernia repair and gastric bypass. She had naturally delivered 3 children. The clinical examination showed a bloated abdomen with a uterus slightly increased in volume. The blood sample was normal.

The pelvic MRI (Figure 7) revealed a 140-mm uterus with an 83×78×65 mm heterogeneous fibroid with many areas of degeneration and 4 other small fibroids – some fleshy parts were the seat of a less marked enhancement and a restriction of diffusion.

The hepatic MRI (Figure 8) detected a unique tumor on the liver: hypointense on T1-weighted imaging (Figure 8A) and hyperintense on T2-weighted imaging (Figure 8B). Contrast-enhanced MRI (Figure 8D–8F) demonstrated no uptake in the arterial phase (Figure 8D). Heterogeneous uptake was observed in the portal phase (Figure 8E). The delayed phase demonstrated enhancements (Figure 8F).

A hysterectomy was performed, and the analysis of the specimen showed a 70-mm lesion in the uterine dome with numerous foci of necrosis and invasion on more than half of the myometrium (Figure 9). Unfortunately, uterine invasion occurred during the extraction of the tumor.

This high-grade sarcoma was composed of neoplastic cells made up of an eosinophilic cytoplasm distributed in clusters or geographic pattern with tongue-shaped infiltration of the wall, resembling a stromal sarcoma (Figure 10). Focally, we found giant, rhabdoid, and mildly fusiform cells with rare deposits of melanocytic pigments. Many lymphatic permeations and emboli were observed (Figure 11). Immunohistochemistry (Figure 12) showed a mixed myomelanocytic phenotype with a strong positivity for HMB-45. The smooth-muscle marker H-Caldesmon was focally positive, and desmin was largely negative or focally positive. Rare cells were marked by CD10, CD117, and cytokeratin.

The extension assessment was completed with a positron emission tomography (PET) scan: 2 hypermetabolic pulmonary nodules were observed in the apical (standardized uptake value [SUV] max=4) and lateral lobe (SUV max=1.7) of the right lung. We also found a 30×29 mm hypermetabolic hepatic lesion on segments V and VI (SUV max=6.7) on MRI (T1 hypersignal, T2 hyposignal). We noticed a hypervascular enhancement with washout with diffusion restriction and satellite perfusion disorders at hepatic arterial phase injury disappearing on late phases. A hepatic biopsy performed on segment VI confirmed a liver metastasis, showing the histologic aspect of PEComa – sheet cells separated by a rich vascularization, with nuclear pleomorphism and a pale or eosinophilic clear cytoplasm – and strong HMB45 immunostaining was also observed.

A search for molecular alterations in 117 genes with next-generation sequencing showed: variant p.(Gln52*) and variant p.(Gly266Arg) of the TP53 gene (Tumor Protein 53), variant p.(Glu272*) of the Tuberous Sclerosis Complex 1 (TSC1) gene, and variant p.(Ser2017Leufs*33) of ATRX gene (Alpha-Thalassemia Retardation X-linked). There were also variants of uncertain clinical significance: BRCA2, GNAS, RET, and TSC2. No fusion transcript was detected among 61 genes.

Targeted sirolimus therapy (4 mg/d) was started 2 months after surgery. The plasma level after 20 days of treatment was 7.1 ng/mL less than the recommended plasma drug level (optimal value 14–920 ng/mL) [11]. Therefore, the dose was increased to 6 mg/day 2 months after initiation of therapy.

A CT scan 5 months after surgery showed regression of the pulmonary nodules. The hepatic lesion had responded with a post-therapeutic necrosis well characterized in the MRI, but with persistence of peripheral arterial enhancement of the lower portion. The dose control showed an optimal plasma drug level at 17.5 ng/mL but with appearance of arthralgia. We then decided to decrease the dose to 5 mg/day. The patient is still in relatively good health 8 months after the procedure.

Discussion

MORPHOLOGICAL FEATURES:

According to the literature, PEComa are generally voluminous (mean diameter of 7–8 cm) [12,14] and present the following imaging features: well-defined borders, regular shape, intense contrast enhancement, heterogeneously enhanced on arterial and venous phases and slight hypodensity on the delayed phase with CT scan and MRI with hypointensity on T1-weighted imaging and hyperintensity on T2-weighted imaging [12]. Nevertheless, these findings are not specific enough to make the diagnosis of PEComa by imaging examination alone, but can help identify the origin and the extension of the mass [10].

IMMUNOHISTOCHEMICAL FINDINGS:

Besides the epithelioid pattern, the other features of PEComa include pleomorphism characterized by multinucleate giant cells and spider cells, macronucleoli, intranuclear pseudo-inclusion, and melanin pigment [1,13]. However, the differential diagnosis with leiomyosarcoma is still challenging in terms of histopathology, since they can both present mixed pattern epithelioid and spindle-shaped cells, historically called group A and group B, respectively [4,5,7]. Immunohistochemistry is essential to correctly interpret the pathological findings: Fitzpatrick et al [10] summarized the main characteristics of PEComas and other malignant primary high-grade sarcomas of similar presentation (Table 1).

According to Schoolmeester et al [14], immunohistochemistry is the best tool for diagnosis, since 90% of PEComas concomitantly express at least 2 melanocytic markers (HMB-45, Melan-A, and microphthalmia-associated transcription tactor (MiTF), and 1 smooth-muscle marker (actin, desmin, H-Caldesmon) [14]. As described by Folpe et al [8] and Conlon et al [7], there are 2 groups distinguished by their morphology: a predominant spindle cell pattern, with a strong expression of muscle markers, and a predominant epithelioid pattern, with strong expression of melanocytic markers. Nevertheless, Bennett et al [13] questioned this paradigm—their cohort study showed strong and diffuse expression of desmin and H-Caldesmon, irrespective of the number of clear cells or percentage of spindled components. According to them, 2 melanocytic markers (or 1 melanocytic marker and Cathepsin-K) are enough to render a diagnosis of PEComa [15]. The “essential” WHO criteria for diagnosis of PEComas are of expression of HMB45 or Melan-A and at least 1 myoid marker [5].

Cathepsin-K, a transcriptional target of the MiTF family, might help in differential diagnosis – this marker is as common as HMB-45 in PEComas [7]. This protease was considered by

Schoolmeester et al [14] as a substitute criterion to diagnose patients as being PEComas Melan-A-negative if the appropriate morphology was present.

In the light of anatomopathological and immunohistochemical results of our second patient – strong expression of HMB45, melanocytic pigments, lymphatic permeation, focal positivity for the smooth muscle, and epithelial and stromal markers – we can easily consider it a uterine PEComa with an epithelioid pattern.

However, regarding our first patient, the diagnosis remains uncertain – the strong expression of the estrogen receptor observed here is unusual in uterine PEComas but is still compatible [12]. Progesterone receptors were also observed in the specimen, and these have already been described in PEComas with spindle morphology [4]. The expression of melanocytic markers (HMB45 and Melan-A) was weak and patchy, which is unusual. Other typical features such as capillary-like vasculature surrounding tumor cells and nests (exclusively found in PEComas) and thick-walled blood vessels (ubiquitous in leiomyomas) were not noticed [10,13]. These different observations raise questions since leiomyosarcoma may also have a myomelanocytic immunophenotype [1,7]. To be cautious, we have classified this tumor as a “sarcoma with PEComa-like features” [16].

PROGNOSIS CLASSIFICATION:

In 2005, Folpe et al [8] proposed several prognostic criteria to help classify PEComas: size less than 5 cm and mitotic rate ≤1/50 HPF are suggestive of benignity; and infiltrative lesion, nuclear pleomorphism, necrosis, and vascular invasion are suggestive of malignity. In 2014, Schoolmeester et al [14] proposed a threshold set at 4 high-risk features to categorize PEComa as malignant based on 16 metastatic uterine cases, whereas in 2020 the WHO set the threshold at 3 criteria, distinguishing “uncertain malignant potential” if less than 3 criteria are met and malignant if 3 or more criteria are met [5].

In 2015, Conlon et al proposed a revised prognosis classification more adapted to the reproductive tract PEComas, called “Folpe-modified” [7].

The accuracy for predicting malignant behavior in uterine PEComas using Folpe’s classification [8] and the “Folpe-modified” classification [7] is 69%.

Considering all these prognosis models, it appears that our 2 cases both met the criteria for malignancy with high risk of recurrence and metastases [2,5,7,8,14] (Table 2).

TRANSCRIPTION FACTOR BINDING TO ENHANCER 3 (TFE3) REARRANGEMENT (20% OF PECOMAS): TFE3 is a member of the MiT family of transcription factors, which also includes MiTF, TFEB, and TFEC [7]. Transcriptional up-regulation is obtained through fusion of TFE3, which activates MET signaling [9]. These translocations are commonly considered to be exclusively from the mTOR pathway, but there has been a case report with expression of both mutations [1,7,10,11,17].

PEComas with TFE3 fusions are characterized by predominantly epithelioid pattern clear cell morphology without perivascular distribution and pleomorphism, especially in gynecological subsets, according to Bennett et al [2,15]. Generally, there is positivity for HMB-45 and Melan-A, and negativity for myogenic factors (especially MiTF) [1,6,7,15,16]. TFE3 mediates the expression of Cathepsin-K, and thus may be a useful marker for TFE3-altered PEComas [9].

WHO 2020 has defined as a “desirable” diagnostic criterion for PEComa the detection of a rearrangement of TFE3, assigning them a distinct category named “TFE-associated” [5].

TUBEROUS SCLEROSIS PROTEINS (TSC1/TSC2) MUTATIONS (50–60% OF PECOMAS): Sporadic or tuberous sclerosis of Bourneville-associated mutation (10% of gynecological cases) results in a loss of tuberin or hamartin function. Tuberin (TSC2) forms with the protein product of hamartin (TSC1), a heterodimer called “tuberous sclerosis complex” (TSC), which functions as a tumor suppressor by inhibiting the mechanism of mammalian target of rapamycin (mTOR) pathways [4,7], causing uncontrolled activation of mTOR signaling with potential tumorigenesis [1,2,7,11,16,18,19]. In the literature, TP53 is a coexistent mutation often identified (63%) in TSC2-mutated PEComas [1]. The mutation of ATRX is also associated with malignant PEComas [1].

Unfortunately, our first case was not explored by further molecular analysis such as next-generation sequencing to help in the differential diagnosis. In our second case, we noticed an unusual concurrent mutation – TP53, ATRX, and TSC1 – which confirmed the malignancy of the tumor. According to recent data, the uncommon TSC1 mutation has a poorer prognosis than TSC2 mutation in PEComas [1,19].

TARGETED THERAPY:

Due to the rarity of cases, the treatment of PEComas is still experimental [2,11,3,14]. It seems that surgical cytoreduction followed by adjuvant targeted therapy produces the best results for malignant tumors [6]. A disease-free survival time of 18–36 months is reported in the literature, with a better response noticed in case of gynecological subtypes [1,2,6]. Targeted therapies have emerged on the basis of the 2 distinct pathways mentioned above – TFE3 and mTOR [11,15].

c-MET inhibitors (crizotinib and tivantinib) have already been tested in alveolar soft-tissue sarcomas with TFE3 translocation, and could be a potential therapy for this subset of tumors [2,7,10,13,16,17]. With many more studies proving their effectiveness, mTOR inhibitors have shown promising results in locally advanced, unresectable, or metastatic PEComas with TSC1/2 inactivation [1,2,7,11,16–19]. The objective rate (partial or complete response) of mTOR inhibitor-based regimen is up to 41%, with 9 months of median disease-free survival and 30 months of overall survival, which was significatively better than with conventional chemotherapy [11]. PEComa patients who received cytoreduction surgery and mTOR inhibitors after cycles of failed chemotherapy and radiotherapy was reported to attain 4 years of disease-free survival; mTOR inhibitors are also used to reduce bulky masses before PEComa cytoreductive surgery [6]. Rechallenging with mTOR inhibitors can also result in new responses in patients with recurrence [11]. Adding anti-estrogen therapy was proved to be efficient in case of mTOR inhibitor resistance [1,9]. To obtain the effective dose for treatment, plasma drug monitoring of mTOR inhibitor is recommended in the management of patients to be able to increase the dose when necessary [11].

To date, studies have shown that orally-administered mTOR inhibitors such as sirolimus (1–10 mg/d) and everolimus (5 mg/day) have variable absorption rates, incomplete target suppression, and often require therapeutic drug monitoring. The first prospective, multicenter trial – AMPECT (Advanced Malignant Perivascular Epithelioid Cell Tumors) – investigated the use of a new albumin-bound mTOR inhibitor called “nab-sirolimus” administered intravenously to treat malignant PEComa [16,19]. Phase II trials have shown it has significantly stronger tumor growth inhibition, higher intra-tumoral drug accumulation, and better mTOR inhibition compared to other mTOR inhibitors, with an objective response rate of 39% (especially in case of uterine tumors), a median progression-free survival of 10.6 months, a median overall survival of 53.1 months, and a disease control rate of 71% [16,19]. This kind of drug was also administered as a neoadjuvant therapy: a variable downsizing effect is observed, which usually allows a second surgery to be performed [2,16,19]. Furthermore, no therapeutic drug monitoring was necessary to take account of the few adverse events with high-dose and long-term therapy. Phosphorylated S6 ribosomal protein expression, reflecting the mTOR pathway activation, appears to predict early tumor response to nab-sirolimus [9,16]. Further studies are needed to evaluate the efficacy in oligometastatic patients.

Conclusions

We have reported 2 cases of metastatic PEComa with different clinical features. The diagnosis of PEComa is still a challenge and the treatment of this pathology is experimental, with a poor prognosis in case of malignancy, especially at a metastatic stage. There is an overlap between characteristics of PEComas and other smooth-muscle tumors, and there are currently no pathognomonic finding or highly specific markers.