Ⅰ. INTRODUCTION
Basaloid squamous cell carcinoma (BSCC) is a rare and aggressive variant of squamous cell carcinoma arising in various anatomical sites. This carcinoma predominantly occurs at the base of the tongue, supraglottic larynx, and hypopharynx1). Other cases occur in the oral cavity, oral mucosa, and palate. Similar to the conventional SCC, BSCC is predominant in the elderly population aged 60 to 80, and alcohol and smoking are known risk factors. Clinical findings also appear similar to conventional SCC. In the most previous reports on BSCC, it appears as a flat and slightly elevated lesion with a central ulceration2). The histopathologic appearance is distinct from well- or moderately differentiated SCC, with varying degrees of typical squamous component interspersed with nests of basaloid cells arranged in lobules with prominent peripheral palisading and central foci of comedonecrosis3). This article describes a case history of BSCC of the floor of the mouth with mandibular involvement, and further discusses the appropriate management of such case with reference to the literature review.
Ⅱ. MATERIALS and METHODS
A 52-year-old male patient was referred to our clinic from another university hospital. He complained of pain on the floor of his mouth and tooth mobility. Upon examination, a red proliferative lesion with ulcer on the floor of the mouth and the anterior portion of the mandible was noted (Fig. 1a). The biopsy report from the previous hospital showed that it was basaloid squamous cell carcinoma or adenoid cystic carcinoma. In order to confirm the diagnosis of the lesion, we performed a biopsy on the lesion again, but the diagnosis of squamous cell carcinoma was made. The patient has been smoking one to two packs per day for 30 years. He appeared his stated age without any signs of cachexia. There was a 4- cm to 6-cm sized red proliferative lesion with ulcer on the floor of the mouth, and the lesion extended to the lower anterior gingiva, which resulted in severe tooth mobility. Right submandibular lymphadenopathy was palpable. Panoramic radiograph showed ill-defined osteolytic lesion on the #31-35 site (Fig. 1b). CT and MRI scans presented enhancing soft tissue density around the left anterior mandible, extending to both sublingual space and left tongue base, as well as bony erosive change of symphysis and left alveolar process of the mandible (Fig. 1-c, d). On PET-CT examination, abnormally elevated FDG uptake was observed at the floor of the mouth (SUVmax: 17.1) and in both Level IB LNs (SUVmax was measured at the right (11.9) and left (3.2) (Fig. 1-e, f). Laboratory testing, including a complete blood count with differential, chemistries with liver and renal function and electrolytes, total protein, albumin, quantitative immunoglobulins, erythrocyte sedimentation rate, lactate dehydrogenase (LDH), ferritin, uric acid, and urinalysis, was performed. The diagnosis of a grade IV squamous cell carcinoma (cT4aN2cMx) was made. The planned treatment was segmental mandibulectomy with supraomohyoid neck dissection and mandible reconstruction with left fibular free flap under general anesthesia, followed by radiotherapy (Fig. 2). The operation was successful. The patient underwent radiotherapy with 50 Gy fractionated over 6 weeks.
Histopathological examination on the tumor lesion revealed that tumor cells were growing and forming a nodule. There were discrete cell boundaries, abundant eosinophilic cytoplasm, and a large number of tumor cells, in which the nucleus was very distinct and the nucleoli were well visible. Nuclear hyperchromatism and pleomorphism were evident, and many mitoses were observed. Most of the papillae were thought to be well-differentiated squamous cells. Meanwhile, other regional histologic findings were very different from the histologic findings that showed features of squamous cell carcinoma at the same site. The degree of differentiation of the tumor cells was different, forming cell nest or lobule and infiltrative growth. Comedo-type necrosis was observed. Concurrent with the above findings, a diagnosis of BSCC (pT4aN2cM0) was given by the oral pathology specialist (Fig. 3).
Ⅲ. RESULTS and DISCUSSION
Although the origin of BSCC has not been elucidated yet, it is believed to have originated from omnipotent cells present in the basal layer of the squamous epithelia according to the WHO classification and Wain, who reported this carcinoma for the first time in 1986. Histologically, the basaloid carcinoma is biphasic, and it consists of a basaloid component and a squamous component, accompanied by comedo-type necrosis, which is a form of necrotic remnant. A biphasic feature can make it difficult to differentiate if there is only one component. Therefore, a good biopsy technique is very important. Deep (full thickness) and large sample enough to allow proper examination is needed. In addition, multiple biopsies may be necessary for a diagnosis. The oropharyngeal subset of BSCC is highly associated with an HPV-positive status4,5).
The supposed higher clinical aggressiveness of BSCC compared with the conventional SCC remains a continuous matter of debate. In 2008, Thariat summarized the previous 24 studies on BSCC, 11 of which showed a bad prognosis, and the rest of the studies showed no difference. The most common metastatic organ was the lungs6,7). In an analysis of 92 patients with BSCC of the oral cavity published by Fritsch in 2014, BSCC in the oral cavity showed a higher grade and clinical stage than the typical SCC at the time of diagnosis. However, there was no statistically significant difference in the survival rates8).
Occasionally, the clinical status at diagnosis and the evolution of BSCCs seem to be especially aggressive2,8,9). The prognosis for lymph node-positive patients with BSCC who received RT was comparable to the prognosis for patients with well or moderately differentiated SCC and poorly differentiated SCC7). Radiosensitivity in the primary tumor, which was evaluated by local control, appeared similar7). Two small case-control studies of BSCC versus SCC of the head and neck reached different conclusions, one suggesting a detriment in survival, and the other with no statistical difference from moderate or poorly differentiated SCC9). After controlling for disease and treatment variables, including neck dissection and radiotherapy, BSCC did not have an independent adverse prognostic effect on the overall survival10).
Basaloid squamous cell carcinoma (BSCC) is a biphasic variant of SCC with both basaloid and squamous cell histology. When basaloid squamous cell carcinoma (BSCC) was first introduced at the other institute, it was aggressive in prognosis compared to a conventional SCC. However, a recent report showed that there is no significant difference in the prognosis. The efficacy of chemotherapy is unclear, but it has been found to be sensitive to radiotherapy. Due to the lack of accumulated research, close follow up and continuous research are deemed necessary.
Treatment that focuses on the stage of the tumor is appropriate, not the emphasis on the difference of histology between BSCC and SCC. A periodic follow-up observation is also very important due to the occurrence of distant metastasis to the lungs. Patients with BSCC at the floor of mouth with mandibular involvement have healed well after the operation and radiotherapy, and they are currently under close follow up.
