Osteoblastic Osteosarcoma With Diverse Histomorphology: Diagnostic Insights From SATB2 and CD56 Immunoexpression

INTRODUCTION

Osteosarcoma (OS), one of the most common primary malignant bone tumours, frequently arises from pre-existing skeletal abnormalities. Other recognised risk factors include rapid bone growth and germline mutations affecting tumour suppressor pathways, such as inactivation of the retinoblastoma gene and hereditary cancer predisposition syndromes (Li-Fraumeni and Rothmund-Thomson). Prior exposure to ionising radiation further contributes to OS pathogenesis. The World Health Organization classifies bone tumours according to anatomical site, biological behaviour, and the extent of cellular atypia. Although the majority of OSs develop within the long bones of the appendicular skeleton, 6% to 13% originate in the craniofacial region, presenting diagnostic and therapeutic challenges.^[1,2] Osteoid formation is a key diagnostic feature of this malignant connective tissue tumour. Jaw osteosarcomas (JOS) frequently occur in the maxillary alveolar ridge and the body of the mandible. Patients generally present with swelling and pain. The prognosis is influenced by multiple factors, including the timing of diagnosis, the extent of tumour resection, age of the patient, and the anatomic location of the tumour.^[3,4] This article presents a case of OS in a 59-year-old male patient, who presented with a nodular growth on the posterior maxillary alveolar crest, with clinical, radiographic, histopathological, and immunohistochemical (IHC) findings.

CASE REPORT

A 59-year-old male patient presented to our dental college with a complaint of a growth in the upper right posterior region that had been present for one week. The patient had a history of hypertension for the past 4 years and was on medication. No malaise or fever was noted at the time of examination, and there was no significant family history or known drug allergies. He had recently visited a local dentist, and there was no history of trauma. The patient was known to have been consuming alcohol for 30 years and smoked beedis, having quit 20 years ago. On extra-oral examination, the submandibular lymph nodes were hard and tender on palpation, fixed to the underlying tissue. The patient underwent fine needle aspiration cytology (FNAC) of the submandibular lymph nodes, and the pathology report indicated a pleomorphic sarcoma. Intra-oral examination revealed a nodular growth, approximately 3 cm × 4 cm in size, protruding from the right maxillary alveolar ridge, covered with slough [Figure 1].

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Figure 1:

A nodular growth measuring approximately 3 cm × 4 cm on the right maxillary alveolar ridge (red arrow).

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The base of the lesion was pedunculated and non-tender on palpation. The patient’s maxilla was completely edentulous, with only a few remaining teeth in the mandible. A panoramic radiograph revealed a soft tissue growth shadow, appearing as a hazy radiopaque mass, measuring approximately 39 × 29 mm in size, located near the maxillary alveolar crest on the right side [Figure 2a]. The gross specimen was greyish-black in appearance and soft in consistency, measuring 2.8 cm × 2.3 cm × 1.5 cm [Figure 2b]. Histopathology revealed dense cellular connective tissue predominantly composed of spindle cells, which were arranged haphazardly [Figure 3a]. The lesional cells exhibited nuclear hyperchromatism, pleomorphism, and mitotic figures [Figure 3b]. Certain areas showed giant cells surrounded by eosinophils. Areas of osteoid formation were also evident. Other cells present included epithelioid and histiocytoid-like cells [Figure 3c]. The tissue was sent for further IHC panel study. The marker results were focal positive for smooth muscle actin (SMA) and epithelial membrane antigen (EMA), positive for special AT-rich sequence-binding protein 2 (SATB2) and cluster of differentiation (CD56) also known as neural cell adhesion molecule (NCAM), Ki 67 a nuclear protein associated with cell proliferation showed a proliferative index of 30-40% with all other markers were negative. The IHC profile was favourable for osteoblastic OS [Figures 4a and 4b] [Table 1]. The patient underwent a maxillectomy with radical neck dissection of the right side, followed by six cycles of adjuvant chemotherapy that comprised adriamycin, holoxan, and mesna. Recurrence was noted after a year, for which the patient underwent a wide local excision for locoregional recurrence.

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Figure 2a:

Panoramic radiograph (red arrow) showing the shadow of the soft tissue growth appearing as a hazy radiopaque mass measuring approximately 38.9 × 29.1 mm (red lines).

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Figure 2b:

Gross pathology specimen measuring 2.8 cm × 2.3 cm × 1.5 cm.

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Figure 3a:

Photomicrographs of osteoblastic osteosarcoma (red arrows) stained with haematoxylin and eosin (H&E). Spindle-shaped cells are arranged in fascicles. (Magnification 10x).

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Figure 3b:

Atypical osteoblasts (red arrows) exhibiting considerable variation in size and shape with large, deeply staining nuclei. The neoplastic cells are close to the matrix of osteoid formations. (Magnification 10x). Haematoxylin and eosin stain.

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Figure 3c:

Multinucleated giant cells, histiocytes, atypical mitoses, and necrosis (Mag 40x). Haematoxylin and eosin stain.

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Figure 4a:

Immunoreactivity showing nuclear positivity for SATB2 using a monoclonal antibody (clone EP281, dilution 1:100) with HRP-polymer method (Mag 40x).

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Figure 4b:

Immunoreactivity showing membranous positivity for CD56 using a monoclonal antibody (clone 123C3, dilution 1:100) with HRP-polymer detection system (Mag 40x).

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DISCUSSION

The 5-year survival rate for appendicular OS is approximately 70%. JOS generally has a more favourable prognosis and tends to present at an older age compared to OSs of the long bones. In this case, the patient is in his late 5^th decade, which is slightly beyond the typical age range for JOS, and the patient had no known predisposing factors for the development of OS.^[5] A review study on the Indian population found a higher incidence of JOS in the mandible than in the maxilla. The study also observed a male predilection for cases in the maxilla, while mandibular cases showed equal sex distribution. Several other studies have demonstrated a greater prevalence in the maxilla, frequently associated with a female predominance.^[6-8] One of the histopathological differential diagnoses in this case was spindle cell carcinoma, characterised predominantly by atypical spindle cell proliferation. However, there was no histological evidence of squamous epithelial differentiation, epithelial dysplasia, or invasion originating from the surface epithelium. OSs are generally negative for p63, making it easier to diagnose over epithelial lesions. It sometimes shows focal staining in some mesenchymal tumours, including OS. This reflects nonspecific expression rather than true epithelial differentiation. Rare variants such as epithelioid OS, metastatic squamous cell carcinoma also show focal p63 positivity, due to partial epithelial differentiation. These tumours can also express low levels of cytokeratin (CK) or EMA. In our case, the IHC panel showed negativity for p63 and focal positivity for EMA. However, both high molecular weight cytokeratins (HMWCKs) and Cytokeratin (CK) were negative, which is unusual for a typical epithelial lesion. While EMA is commonly used as an adjunct to CK in identifying tumours with epithelial differentiation, its focal expression in the absence of CK limits the diagnostic implication of true epithelial origin.^[9]

The histologic subtypes of OS central include conventional, telangiectatic, small cell, epithelioid, fibroblastic, osteoblastoma, chondroblastoma-like, fibro-histiocytic, and giant cell-rich.^[5,7] The predominant cellular features in our case included fibroblastic, osteoblastic, epithelioid, and histiocytic giant cell-rich types, with the exception of the small cell and chondroblastoma-like types. The neoplastic cells with an osteoblastic appearance are believed to be undifferentiated mesenchymal cells that give rise to fibroblasts or osteoblasts.^[7,8] Since our case displayed numerous atypical cells with mitoses along with histiocyte-like cells, inflammatory cells, and spindle cells, the other histopathological differential diagnosis was a pleomorphic sarcoma, also reported from FNAC. The 4th edition of the WHO 2013 classification of soft tissue & bone tumours has renamed malignant fibrous histiocytoma, replacing it with pleomorphic sarcoma, undifferentiated.^[10]

Several spindle cell lesions can mimic OS, particularly when malignant osteoid is sparse or absent on histological sections. These include fibrosarcoma of bone, which shows a herringbone pattern of uniform spindle cells without osteoid production. Others include leiomyosarcoma of bone, positive for SMA and Desmin, and malignant peripheral nerve sheath tumour, often showing focal S-100 positivity. Focal SMA expression helps exclude other differential diagnoses like leiomyosarcoma or myofibrosarcoma, which show diffuse and strong SMA positivity. Desmin helps exclude sarcomas of muscle origin, as its absence suggests non-muscle differentiation. Myogenin and myogenic differentiation 1 (MyoD1) are specific markers for rhabdomyosarcoma and aid in distinguishing it from other spindle cell tumours. Although rare, focal expression of these markers occurs in non-rhabdomyosarcoma tumours. OS can show focal SMA positivity but typically lacks desmin and caldesmon expression, thus helping in ruling out true smooth muscle differentiation.^[11-13] In our case, both Desmin and Caldesmon were negative with focal SMA positivity, suggesting either limited myofibroblastic differentiation or reflecting reactive stromal cells. Synaptophysin and Chromogranin A are generally positive in neuroendocrine tumours. If S100 is positive, it suggests cartilaginous, neural, or melanocytic differentiation and should be confirmed with other markers such as Human Melanoma Black-45 (HMB-45) and melanocyte-specific differentiation antigen (Melan-A) to rule out entities like melanoma or clear cell sarcoma. In our case, all three markers, S100, HMB45, and Melan-A, were negative, ruling out melanocytic differentiation, including melanoma and clear cell sarcoma.^[14-16]

The marker study of CD34 was negative in our case. It is used to assess tumour vasculature, which is often increased in OS. Studies have shown that CD34 expression correlates with microvessel density, supporting its role in tumour angiogenesis. Furthermore, elevated CD34 expression has been associated with tumour progression and metastasis, highlighting its potential as a prognostic marker for disease advancement.^[17]

Research studies show that in bone tumours, including OS, the level of Ki-67 expression correlates with the degree of malignancy. Higher Ki-67 levels were observed in more aggressive tumours, suggesting its utility in diagnostic and prognostic evaluations.

In our case, the Ki-67 index was 30-40%, indicating a moderate to high level of proliferative activity, suggestive of a more aggressive tumour behaviour and poor prognosis.^[18,19] OS cells do not express leukocyte common antigen (LCA), a marker specific to hematopoietic cells. Therefore, LCA negativity, likewise in our case, helps exclude lymphoid malignancies such as non-Hodgkin lymphoma.^[20]

CD56 is expressed in a variety of normal tissues and tumours, including neurons, natural killer cells, also observed in osteoblasts and OSs, but not in Ewing’s sarcoma or chondrosarcoma. This suggests that CD56 serves as a marker for osteoblastic differentiation.^[21,22] Studies have shown that SATB2 is expressed in a high percentage of OS cases. A study evaluating SATB2 expression in 2 cases of cutaneous osteoblastic OS found immunoreactivity for SATB2, supporting its utility as a marker for osteoblastic OS. Another study reported SATB2 positivity in 92.6% of OS cases, particularly in osteoblastic subtypes. Though SATB2 is not specific for osteoblastic differentiation, when minimal osteoid formation is present, comparing it with other markers, it can be beneficial in diagnosing osteoblastic OS.^[23,24]

CONCLUSION

Malignant mesenchymal neoplasms, such as OS, exhibit a wide range of histopathological features due to their origin from a common mesenchymal stem cell lineage, often resulting in diagnostic challenges. Patients with JOS may experience recurrences; however, these tend to be less aggressive and have a better prognosis compared to other forms of OS. Over the years, survival rates have been gradually improving as patients receive more effective combination chemotherapy regimens.