Spindle cell carcinoma (SpCC), also known as sarcomatoid carcinoma or pseudosarcoma, of head and neck is a rare neoplasm. SpCC is known as a high malignant variant of squamous cell carcinoma, which is composed of conventional squamous cell carcinoma component, either in-situ and/or invasive and malignant spindle component with sarcomatous appearance. Although it is generally accepted that SpCC is a monoclonal epithelial neoplasm 12345, and the sarcomatous components are derived from squamous epithelium with divergent mesenchymal differentiation 6, the diagnosis, classification and management of this tumor infrequently may become subject matter deluded of its histological variety in sarcomatous components. These sarcomatous components commonly resemble to fibrosarcoma or malignant histiocytoma 78, and while rare, foci resembling to chondrosarcoma and/or osteosarcima differentiation may be observed 9.

This is a case report of a spindle cell carcinoma of gingival mucosa presenting with bone-like calcified materials.

A 71-year-old Japanese male patient was referred to the Okayama University Hospital, complaining the swelling at the left side of the mandibular molar region. The lesion was 44 × 29 mm in size, exophytic with rough and irregular surface. The patient's medical and family histories were unremarkable.

Clinically, the lesion was elastic soft and fragile, and the surface of the lesion was ulcerated [Fig. 1]. The margin of the lesion was clear, and MRI scan revealed no invasion into circumjacent tissues [Fig. 2]. Moreover, invasion into the mandibular bone was not prominent on the CT images. With the suspicion of poorly differentiated squamous cell carcinoma from the biopsy, surgical resection with neck dissection was performed. The lesion was a fragile mass, grayish-white in color [Fig. 3].

No tumor cells were observed around the surgical margin, and lymph node metastasis was not observed. No recurrence or metastasis was detected since surgery so far.

Histologically, the tumor showed biphasic appearance. The bulk of the tumor was composed of invasive, spindle shape cells, which arranged irregularly with bundle formation resembling to fibrosarcoma. Together with the spindle shape tumor cells, proliferation of polygonal epithelial cells were observed, forming tumor nests with distinct keratinization similar to cancer nest observed in well differentiated squamous cell carcinoma. In some areas, spindle shape cells were transitional to the epithelial cancer nest-like structure. The stromal cells were intermingled with the spindle shape cells, showing myxoid appearance. In some areas, spatters of calcified, bone-like materials were observed in between the malignant spindle cells, which showed osteosarcimatous appearance [Fig. 4]. From all these histological findings, the lesion was diagnosed as spindle cell carcinoma (SpCC) with osteosarcomatous differentiation.

To confirm the diagnosis, immunohistochemistry was performed according to avidin-biotin-peroxidase complex (ABC) method. The detail of the antibodies used for immunohistochemistry is summarized in Table 1.

Immunohistochemistry revealed that spindle shape cells showed positive reaction for cytokeratins, vimentin, negative reaction for S-100 protein and desmin, squamous cell carcinoma-like nest forming epithelial components showed positive reaction for cytokeratins, both low- and high-molecular weight, negative for vimentin, S-100 and desmin. Alpha smooth muscle actin (αSMA) was vaguely positive in both spindle shape cells and epithelial cells. The cells around bone-like calcified materials showed positive reaction for low-molecular weight cytokeratin and vimentin, osteopontin was only positive in the bone matrix-like area. Cancer cells did not show positive reaction for osteopontin, bone morphogenetic protein (BMP) -2 or BMP-4. Ki-67 index was around 30% at a maximum, but that of the cells around bone-like materials was lower [Fig. 5]. Thus the bone-like materials were considered as metaplastic bone formation.

SpCC is a rare variant of squamous cell carcinoma. Its most frequently affected sites is larynx, however, it may infrequently occur in various organs; gingiva 210, tongue 1112, upper aerodigestive tract including hypopharynx and nasal cavity 61314, esophagus, skin and breast 15.

It is generally understood that the diagnosis of SpCC requires the demonstration of both components 16. In accord with this criterion, typical histology of SpCC was observed in the present case, which was composed of conventional squamous cell carcinoma component and spindle shape cells with sarcomatous appearance.

However, the existence of bone-like calcified materials was the uncommon, controversial finding for SpCC in oral mucosa. To the best of our knowledge, this finding was not described in previous report. In the immunohistochemical examination, both epithelial component and spindle shape cell component showed positive reaction for cytokeratins to a varying degree, but vimentin positive cells were limited to the spindle shape cell component. These results were consistent to the previous reports 114171819. The cells around the materials were vimentin-positive low activity cells, and cancer cells did not show positive reaction for neither BMP-2 nor BMP-4, which indicates these materials were formed by mesenchymal metaplasia of the stromal cells, but not by the tumor cells itself.

Although the incidence of osseous metaplasia is rare finding in oral SpCC, it is occasionally observed in that of larynx 8. While also rare, the formation of bone-like and/or cartilage-like materials by the metaplasia of stromal cells is often reported in various kind of carcinomas, such as laryngeal cancer 20, esophageal cancer 2122, colon cancer 232425, lung cancer 26, and breast cancer 27. The histogenesis of the osseous and/or cartilaginous metaplasia in the carcinoma has been come up to debate so far. The biological mechanism of these metaplastic changes is considered to be caused by stromal activation associated with human-host interface 20. Although some report implies the formation of these materials is related to radiation therapy 21, the mechanism of stromal metaplasia is still unclear. Moreover, the affection of these metaplastic bone or cartilage on the clinical features, prognosis, and response to radiation therapy or chemotherapy are not well established.

In summary, we reported a unique of SpCC with calcified bone-like materials in the gingiva, which is a very rare case in the literature.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

SpCC: Spindle cell carcinoma

The authors declare that they have no competing interests.

NK, HN and RT carried out the case study, discussed and reviewed the literature and prepare the manuscript. GT and JM contributed to the collection of clinical and/or radiological data and discussion. GM, JA and AS participated in review process and carried out critical revision of the manuscript.