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Characteristics of Laryngeal Osteosarcoma: A Critical Review

Laryngeal sarcomas constitute an extremely rare entity among head and neck malignancies. Furthermore, most of them are chondrosarcomas, and the osteogenic form remains a true rarity. In general, there is a lack of information on the characteristics of laryngeal osteosarcoma. Thus, we sought to critically review the existing world literature on laryngeal osteosarcoma in order to develop a more accurate clinicopathological profile of this malignancy. Laryngeal osteosarcoma has a predilection for elderly male patients, as 87% were male in the present series and the mean age was 62 years (range 32–80), and without a direct association with tobacco exposure. Osteosarcoma of the larynx is typically a highly malignant neoplasm that metastasizes early, has a propensity for hematogenous spread and also has a marked tendency to recur. Twelve (41%) out of the 29 cases in the present review with follow-up data had metastatic disease. The aspects that distinguish osteosarcoma from its differential diagnostic alternatives are discussed in this review.


INTRODUCTION
Despite being the most common primary malignant neoplasm of the bony skeleton, osteosarcoma is one of the rarest malignant mesenchymal neoplasms of the larynx. Sarcomas encountered in the larynx are usually chondrosarcomas. Therefore, even physicians in referral-based academic centers of pathology or otorhinolaryngology-head and neck surgery may encounter only a single patient with a true laryngeal osteosarcoma in their entire career. Of note, we searched the REFCOR database (réseau d'Expertise Français sur les Cancers ORL Rares [French Network of Rare Head and Neck Tumors]) in order to find cases to report in the present review. The REFCOR has been registering rare head and neck cancers, i.e., rare cancers of the aerodigestive tract excluding squamous cell carcinoma and undifferentiated nasopharyngeal carcinoma, and cancers of the salivary glands, ear, nasal cavities, and sinus, since 2008. Out of the 7530 patients registered up to August 2019, only 54 osteosarcoma cases were diagnosed, and none of these was located in the larynx.
Laryngeal osteosarcoma was first described by Jackson and Jackson in 1942 without histological documentation [1]. In 1946, Clerf et al. reported eight cases of sarcoma of the larynx, and one of these was classified as fibro-osteosarcoma, but the photomicrograph of the tumor was not convincing [2]. The first welldocumented case of laryngeal osteosarcoma was described by Sprinkle et al. in 1966 [3]. Of note, in 1974, the textbook Tumors of the Head and Neck: Clinical and Pathological Considerations by Batsakis concluded that no authentic case of osteosarcoma in the upper respiratory tract, including the larynx, had been reported at that time [4]. In 2017, Bennion et al. reported 33 laryngeal osteosarcomas having been reported in the English literature since 1942, but many of the reports listed in their review, including their own cases, did not present pathological documentation [5].
It is noteworthy that morphological features of sarcomas typically represent a heterogeneous variation in morphology. This will lead to challenging differential diagnostic considerations, especially when the obtained biopsies remain small. In contrast to a low-grade chondrosarcoma-in which a limited biopsy specimen may still leave open the question of the malignant nature of that lesion-it is usually quite apparent for the pathologist that a laryngeal osteosarcoma specimen represents a highgrade malignancy. More importantly, the precise subclassification of the malignancy will need to be determined.
The existing reports of laryngeal osteosarcoma cases do not consistently include pathological documentation that would allow critical evaluation of the final pathological diagnosis. Therefore, our primary aim was to create a current series of all the published laryngeal osteosarcoma cases by critically evaluating the published reports of this rare malignancy and to include only those cases with adequate pathological description of the findings. The secondary aim was to obtain comprehensive information regarding the characteristics of these neoplasms to enable a discussion of possibilities for enhancing their diagnostic accuracy.

METHODS
We conducted a literature search in the PubMed database using the following keywords: ''Laryngeal'' OR ''Larynx'' AND ''Osteosarcoma''. The search covered all years from the origin of the database until 31 December 2019. The Preferred Reporting Items for Systematic Review and Meta-Analysis (https://www.equatornetwork.org/) methodology was applied. A total of 61 hits were retrieved (Fig. 1). Of these, 30 publications were relevant as having reported a new case/s of laryngeal osteosarcoma (N = 33) that met the inclusion criteria of providing proper pathological evaluation and photomicrographic documentation of the finding. Cases that did not meet these inclusion criteria were excluded. This article is based on previously conducted studies and does not contain any studies with human participants or animals performed by any of the authors.

Clinical Features of the Reported Cases in the Literature
Many reports indicate that this neoplasm occurs in men in their sixth and eighth decades of life, and that the lesion is not directly associated with alcohol or tobacco exposure [6,7]. Laskin et al. and Sheen et al. reported two patients with a history of radiotherapy prior to the development of laryngeal osteosarcoma [8,9]. These tumors usually arise from the vocal cord and cricoid cartilage. Therefore, the most common symptoms are hoarseness, dyspnea, and obstruction. The tumors included in this review and with information on the exact location (N = 22) involved either subglottic [2], supraglottic [3] or transglottic [2] structures, vocal cords [10], or thyroid and/or cricoid cartilages [6].
Osteosarcoma is typically a highly malignant neoplasm that metastasizes early, with a propensity for hematogenous spread and also a marked tendency to recur. There are reports of metastases to regional lymph nodes, but these remain rare, and instead, hematogenous spread to the lungs is the main route. In the present review, 12 out of the 33 patients were diagnosed with distant metastases, most frequently in the lungs. Seventeen out of the 25 patients with follow-up data available in the published case reports had experienced persistent or early recurrent disease, typically within 1-2 years.

Pathology of Laryngeal Osteosarcoma
Macroscopically, the neoplasm is mainly polypoid or exophytic in appearance but may also mimic other sarcomas. The gross specimen is typically grainy and, in some areas, difficult or impossible to cut with a scalpel because of its ossification. The tissue may have a variable color ranging from yellow to brown or red.
Microscopically, the tumor is composed of frankly malignant, spindle-shaped mesenchymal cells, associated with osteoid and immature neoplastic bone formation, as was shown in the reviewed reports (Fig. 2). The nuclei show considerable hyperchromasia or pleomorphism, and mitoses may be numerous. Atypical and bizarre giant cells and multinucleated osteoclast-like cells have been described. Venous invasions may be identified.
Immunohistochemical staining has shown that the neoplasm is positive for vimentin and negative for desmin, S-100 protein, cytokeratin (AE1/AE3, MNF-116, CK5/6, CK7, CK8, CK19, CK20), and epithelial membrane antigen. Both osteonectin and osteocalcin are expressed in osteogenic sarcoma but are not sufficiently specific. However, osteonectin and osteocalcin will highlight osteoid matrix and distinguish it from collagen matrix.
Electron microscopy studies [10][11][12] have shown cells resembling osteoblasts with b Osteoid formation (arrows) by the tumor cells is readily apparent and confirms the diagnosis of osteosarcoma (hematoxylin-eosin). c Another area of the tumorproducing osteoid (arrows) (hematoxylin-eosin) pleomorphic nuclei and nucleoli of variable size within the abundant cytoplasm containing numerous dilated cisternae of rough endoplasmic reticulum. The cells were enveloped by interlacing collagen fibers. Osteoblastic elements predominated but cartilaginous and fibrous tissue could also be found. No desmosomes or other evidence of epithelial differentiation was found in the tumor.

Diagnosis of Laryngeal Osteosarcoma
The definite diagnosis of osteosarcoma depends on the identification of osteoid production by malignant cells in the biopsy sample, as was shown in the reviewed reports. The differential diagnosis includes spindle-cell squamous carcinoma with osteoid differentiation, chondrosarcoma, malignant fibrous histiocytoma, fibrosarcoma, and myositis ossificans affecting the larynx. Spindle-cell squamous carcinoma may contain benign and rarely malignant osteoid areas [13]. Therefore, older reports of laryngeal osteosarcoma may represent spindlecell squamous carcinoma with osteoid formation. Any bone-producing malignant mesenchymal lesion should at first be suspected as a spindle-cell carcinoma. The presence of islands of carcinoma in situ or microinfiltrating carcinoma excludes the diagnosis of osteosarcoma.
In osteogenic sarcoma, clearly sarcomatous areas are present, and the ''zonal phenomenon''-which is characterized by a central cellular area, an intermediate zone of osteoid formation, and a peripheral shell of highly organized bone-is absent. The phenomenon of formation of mature bone is most prominent in the periphery of the lesion and is an important criterion for differentiating myositis ossificans from osteogenic sarcoma. In this latter lesion, mature osteoids are located in the center of neoplasm, and neoplastic mesenchymal cellsthat form the osteoids-are in the periphery.
Osteogenic sarcoma metastatic to larynx has also been reported [14,15]. This unlikely event can be ruled out with clinical assessment of the patient.

Treatment and Prognosis
Wide local resection with clear margins, which typically warrants total laryngectomy, remains the treatment of choice for laryngeal osteosarcoma to achieve local control and long-term Laryngeal osteosarcoma usually results in death in less than 2 years from either extensive local disease or pulmonary metastases    In the present review, five out of the 33 patients had no reported follow-up data. Eleven out of the 28 patients with follow-up data available were alive with no evidence of disease after a variable follow-up time (range 9 months to 8 years).
The important features of laryngeal osteosarcoma are summarized in Table 1. A summary of the reported laryngeal osteosarcoma cases is shown in Table 2, with the first case published in 1966 [3] and the last in 2019 [38]. Table 3 provides a description of the cases that have been reported without pathological documentation.

CONCLUSIONS
True laryngeal osteosarcoma remains an extremely rare malignancy. The true incidence of this entity is not known but based on the number of existing well-documented cases (n = 33) in the literature during 1966-2019, it is obviously not encountered at most of the institutions managing laryngeal tumors.
The diagnosis of this highly malignant tumor would preferably warrant an international consultation network including a registry of rare head and neck neoplasms. Electronic platforms for such activities exist. Our review demonstrates that full photomicrographic documentation is essential for the diagnosis and registration of osteosarcoma cases. Furthermore, such a collaborative effort would enable multidisciplinary recommendations for individual management as well. Naturally, management of laryngeal osteosarcoma should be