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Introduction
Retroperitoneal spindle cell neoplasms are rare, diverse tumors (benign or malignant) composed of spindle-shaped cells, challenging to diagnose due to shared features. Spindle cell tumors of the retroperitoneum encompass a broad range of entities, many of them sharing similar microscopic appearances. This is why establishing an accurate diagnosis can be difficult in some cases. Although some tumors appear poorly differentiated, most of them show evidence of specific lineages such as adipocytic, smooth muscle, myofibroblastic or nerve sheath differentiation, along with additional macroscopic, histologic, immunohistochemical or molecular features that aid the diagnosis(1,2).
Case report
We present a case of suspicion of well-differentiated liposarcoma that came in consultation and requested for immunohistochemical confirmation. The pathological material consisted of two paraffin blocks from an incapsulated tumor measuring 9/9/9 cm and resected from the retroperitoneum. The patient was a 50-year-old woman.
Materials and method
Slides obtained from the paraffin blocks, with 4-µm thick sections, were stained with Hematoxylin & Eosin (HE) after a standard procedure. Immunohistochemistry panel was established after histopathological aspects. We performed immunohistochemical tests with LEICA BOND III automatic machine using Leica Bond antibodies for CD34 (QBEnd/10), Desmin (DE-R-11), ER (6F11), PRG (16), Ki67 (MM1), S100 (EP32), and using ABCAM antibodies for MDM2 (2A10), along with DAKO Autostainer Link48 automatic machine using DAKO antibodies for h-Caldesmon (R-CD), CD117 (c-kit).
The microscopic features of the tumor on HE slides were: a proliferation of spindle cells fascicles with eosinophilic cytoplasm and elongated blunt-ended cigar-shaped nuclei (Figure 1).
No necrosis was found, and minimal nuclear atypia was present, with less than 2 mitosis/50 HPF. In this case, an important number of mast cell was noted, haphazardly distributed in the tumor (Figure 2).
These features were highly suggestive of a smooth muscle tumor. Taking into consideration the previous suspicion of well-differentiated liposarcoma rendered in another service, we ordered a large immunohistochemical panel of markers in order to take into consideration all the differential diagnostics of spindle cell neoplasms of retroperitoneum.
Immunohistochemically, the tumor was intensely positive for Desmin and h-Caldesmon (Figure 3).
S100 and MDM2 were negative, excluding well-differentiated and dedifferentiated liposarcoma (S100 and MDM2 are positive in well differentiated liposarcoma), as well as excluding schwannoma and malignant peripheral nerve sheath tumor (MPNST), which are usually at least focally positive for S100(3-5). CD117 was negative in the neoplastic cells, excluding a gastrointestinal stromal tumor (GIST), but was positive in numerous mastocytes (Figure 2).
Hormonal receptors estrogen (ER) and progesterone (PGR) had nuclear expression in the tumor (Figure 4). CD34 was positive in intratumoral vessels, excluding GIST and a solitary fibrous tumor. The proliferation index Ki67 was estimated around 1-3%.
Discussion
The histological and immunohistochemical features fulfilled the criteria for a smooth muscle neoplasm, most probably benign. Leiomyosarcoma was excluded, because the tumor was incapsulated, the mitotic index was low, minimal nuclear atypia was present, and there was no necrosis(6,7). The differential diagnosis of retroperitoneal spindle cell neoplasm was mainly based on a minimal but specific panel of immunohistochemical markers (Table 1).
The particularity of this case consists in an unusual number of mastocytes. This feature is sometimes encountered in a subtype of leiomyoma. After thorough macroscopic, histological and immunohistochemical data correlation, the diagnosis was concluded as a deep leiomyoma, mast-cell rich subtype(8).
It is imperative to obtain sufficient and representative histopathological material in order to establish an appropriate diagnostic, especially in spindle cell neoplasms of the retroperitoneum, which are known to be sarcomas in a significant number of cases (15% of all tissue sarcomas)(1).
The differential diagnosis is based on clinical criteria (age, sex), macroscopic criteria (encapsulation, infiltration in adjacent structures, dimensions) and microscopic features, as well as immunohistochemical characteristics and molecular testing.
Conclusions
When the suspicion of a malignant spindle cell proliferation of the retroperitoneum is rendered, every effort should be made in order to achieve the correct diagnostic by taking into account all the differential diagnostic entities. The case we presented gave us the opportunity to develop the arguments that sustained a benign smooth muscle proliferation, in contradiction with the initial grim diagnosis.
Corresponding author: Florinel Pop E-mail: florinel.pop@spcaroldavila.ro
Conflict of interest: none declared.
Financial support: none declared.
This work is permanently accessible online free of charge and published under the CC-BY licence.
