Case Reports in Oncological Medicine Myoepithelioma: A New Rearrangement Involving the LPP Locus in a Case of Multiple Bone and Soft Tissue Lesions

We report a case of multiple myoepithelioma with synchronous bone and soft tissue tumors, associated with a new genomic alteration of the LPP locus. The lesions occurred in the foot by presenting one lump in the plantar soft tissue, and three lesions were detected in the calcaneus and in the navicular bone. All tumors showed the double immunophenotype of epithelial markers and S100 protein expression. No rearrangement of the EWSR1 and FUS loci was detected as reported in myoepitheliomas. However, molecular karyotyping detected an unbalanced rearrangement of the LPP locus, not involving the HMGA2 locus, which is the most frequent translocation partner observed in benign mesenchymal tumors such as lipomas (of soft tissue as well as parosteal) and pulmonary chondroid hamartoma.


Introduction
Myoepithelial tumors (METs) of soft tissue and bone are rare tumors of uncertain histogenesis. e rst deep tumor was described in the retroperitoneum [1], followed by a large series in 1997 including cases in soft tissue [2]. Rare cases in bone are more recently reported, and these lesions tend to occur in the acral region of the lower limbs usually in middle age male patients [3][4][5][6][7]. Axial localization of METs has to be distinguished from chordoma.
Histologically, METs are made of a homogeneous population of myoepithelial cells. ey could be considered as a part of a continuum with mixed tumors when ductal di erentiation is present. ey may harbor chondroid and bone di erentiation as observed in classical mixed tumors. e diagnosis of MET requires the coexpression of both epithelial markers and S100 protein [8,9]. ey share morphological and immunohistochemical features with their counterparts described in skin and salivary gland.
A di erent genetic pattern distinguishes METs arising in the skin from those in deep soft tissue and bone. EWSR1 (22q12) gene fusions have been detected in half of METs arising in deep soft tissues and in up to 70% cases of intraosseous MET [7,10]. Several partners of EWSR1 are described: POU5F1(6p21.33) (16%), PBX1 (16%), PBX3, ZNF444, ATF1, KLF17, and NFATC2 [10][11][12][13][14][15][16]. e EWSR1-POU5F1 more often occurs in children and young adults while the EWSR1-PBX1 occurs in middle-aged adult patients [11,14]. e tumors of the rst subgroup show a solid or nested growth arrangement of tumor cells showing at least partially a clear appearance of the cytoplasm. e subgroup with EWSR1-PBX1 rearrangement presents a bland sclerotic appearance or clear cell morphology with a di use EMA staining. However, none of the EWSR1-rearranged tumors show the presence of ductal or glandular di erentiation or cartilage/bone matrix formation [10]. Rearrangement of the FUS(16p11) gene has also been reported in rare cases of MET arising in deep soft tissue as well as in bone [15,17]. Two gene partners have been characterized, KLF17 and POU5F1. ese FUS-rearranged tumors also lack ductal di erentiation [15].
PLAG1 (8q12.1) and HMGA2 (12q14.3) rearrangements are the most common genetic events in pleomorphic adenomas [18]. PLAG1 is also found in MET [19,20]. In the study of Anthonescu et al., 3 cutaneous and 10 soft tissue METs (out of a total of 35 tumors) showed the presence of PLAG1 gene rearrangement [19]. All tumors except one showed tubular di erentiation, suggesting that MET with tubuloglandular di erentiation, called mixed tumors of skin or of soft tissue, are genetically linked to their salivary gland counterpart.
We report an unusual observation in a 52-year-old man of a multifocal MET without obvious ductular di erentiation and harboring a new LPP unbalanced rearrangement without EWSR1 and FUS alterations in both soft tissue and bone lesions.

Case Presentation
A 52-year-old patient complained of pain and swelling of the foot. MRI and plain radiography demonstrated a main lesion in the calcaneus, two others in the navicular bone, and a last one in the plantar soft tissue (Figure 1(a)). e main bone lesion was rst investigated by ne needle aspiration. e soft tissue lesion was then resected.

Pathology.
e tumor of the calcaneus measured 4.4 × 3.4 cm (Figure 1(b)), and the other lesions in the medial cuneiform measured 2.2 × 0.9 cm (Figure 1(b)) and 0.5 mm. e one in the soft tissue, resected independently, measured 3.5 × 2.7 cm. On histology, the di erent tumors appeared lobulated and contained plasmacytoid cells arranged in lobules and in large cellular sheets, intermixed with areas of brous and chondromyxoid stroma positive for alcian blue (Figure 1(d)).
ese cells showed mild nuclear pleomorphism and some cysts were observed, but no convincing ductular di erentiation (Figure 1(e)). Some groups of tumor cells were detected in peripheral vascular spaces, without obvious brin but suspicious for vascular emboli (not shown).
Immunohistochemistry demonstrated an intense and di use staining of plasmacytoid cells for the broad-spectrum cytokeratin, S100 protein (Figures 1(g) and 1(h)), and vimentin. A focal staining for GFAP was noticed. EMA was focally positive in the cytoplasm, and a very focal membranous apical staining was also present (Figure 1(f)). ere was a di use nuclear staining for INI1. Alpha-smooth muscle actin and desmin immunostainings were negative. ese results were in favor the diagnosis of a MET. Based on the multiplicity of localizations, a transtibial amputation was decided by the local multidisciplinary committee. Although lesions were multiple and some pictures were suspicious for vascular emboli, the patient had no recurrence or distant metastasis 2 years later. e last follow-up detected small lung lesions, which remained stable and were considered as aspeci c.

Cytogenetics.
Conventional karyotyping detected the same abnormal complex pseudodiploid clone in the soft tissue tumor as in the bone tumor (Figure 2(a)).
FISH experiments were performed to look for rearrangement of genes known to be altered in MET arising in deep soft and bone tissues, EWSR1 and FUS. FISH detected no rearrangement of those loci. Other di erential diagnoses were excluded by FISH: extraskeletal myxoid chondrosarcoma (NR4A3) and alveolar soft part sarcoma (TFE3).
FISH experiments with BAC probes con rmed the 3q27.3-q28 unbalanced rearrangement with the loss of the probe located 5'/centromeric to the LPP locus (Figure 2(b)) but did not detect any rearrangement of the HMGA2 locus which is the most frequently reported partner gene of LPP in di erent benign mesenchymal tumors.

Discussion
MET can occur in various sites, but only 9% of MET occurs in bone. Most of the deep-seated lesions in bone are incidental discoveries. Tumor sites are tibia, ilium, vertebra, maxilla, and sacrum [24][25][26]. As far as we know, only a cutaneous and subcutaneous MET has been reported in the foot [27]. We described here synchronous tumors in two di erent bones of the foot and in the soft tissue of a 52-yearold man with no further aggressive evolution.
is observation is also unusual at the genetic level. We did not detect the rearrangement of the EWSR1 and FUS genes classically involved in METarising in deep soft and bone tissue without ductal di erentiation. Instead, a hitherto unreported rearrangement of the LPP locus was found. e LPP gene is known to be rearranged through chromosomal translocations [28]. e most frequent one is the t(3;12)(q27-q28;q14-q15), which is recurrent in lipomas (of soft as well as parosteal tumor) and fuses LPP with HMGA2 [29]. is translocation is also described in pulmonary chondroid hamartomas [30] and in one case of soft tissue chondroma [31]. ree other LPP-partner genes have been reported in one case of lipoma, HMGA1(6p21) [32], and in 2 di erent 2 Case Reports in Oncological Medicine hematological malignancies: KMT2A(11q23) in a secondary acute leukemia [28] and BCL6(3q27) through a 3q27 interstitial deletion in a primary central nervous system lymphomas [33]. e oncogenic role of LPP remains unclear, while the role of the partner gene seems to be crucial. Several lines of evidence suggest that HMGA2 truncation occurring in the most common t(3;12) fusion gene is implicated in lipomagenesis.
However, the HMGA2-LPP fusion protein retains the transactivation functions of two LPP LIM domains which might contribute to the mesenchymal tumorigenesis by directly a ecting transcriptional regulation processes [34].
Although not rearranged by FISH, we cannot exclude a cryptic insertion of the 5' part of HMGA2 within the LPP locus. e only candidate locus for a gene fusion with LPP may be TRPS1 (8q23.3) whose 3' part is deleted. TRPS1 is known to be associated with tumorigenesis, metastasis, and angiogenesis in several tumors, including osteosarcoma [35]. Unfortunately, it was not possible to further characterize the LPP-partner gene by 3' RACE-PCR or RNASeq.
No ductal di erentiation was present although membranous EMA staining was focally detected. e stroma was focally myxoid but without a mesenchymal cell population as observed in mixed tumors. Recurrent genetic abnormalities involving PLAG1 and HMGA2 have been described in pleomorphic adenomas (mixed tumors) of salivary gland [36]. PLAG1 rearrangements were mainly identi ed in a subset of cutaneous and super cial soft tissue MET tumors, often displaying ductal structures and considered as mixed tumors [10]. PLAG1 has not been tested because of the absence of ductular di erentiation in the tumor.
We describe here a new rearrangement of the LPP (3q27-3q28) locus in synchronous tumors presenting epithelioid features.
e partner gene remains to be characterized. Analysis of the LPP locus should be performed by FISH on MET without EWSR1 or FUS rearrangements and pleomorphic adenomas of salivary gland without PLAG1 and HMGA2 aberrations to de ne the recurrence and the tumor characteristics associated with this new alteration.
Ethical Approval e study was approved by the local ethics committee.

Conflicts of Interest
e authors declare that there are no con icts of interest regarding the publication of this paper.