3 | DISCUSSION
SCC accounts for 90% of tumors in hypopharynx. Other histological types are relatively uncommon. As for ACC, it is extremely rare. Dysphagia is one of the common symptoms related to ACC, especially for solids, which are similar to SCC. Imaging studies, e.g. CT or MRI, contribute to provide anatomic details that are useful for surgical planning, but not to make differentiation from SCC. A tissue diagnosis is required to make the diagnosis. Only few authors reported cases of ACC in hypopharynx.2,3
Furthermore, the pathologic features of basaloid squamous cell carcinoma (BSCC) can be similar to that of ACC. BSCC generally displays certain histological features, such as no presentation of bi-layered structures and basophilic matrix, and diffuse immunopositivity for p63 and p40 in tumuor cells revealed the absence of myoepithelial elements.4 Although it is known that BSCC with adenoid cystic-like features (BSCC-AdC) occurs more commonly in esophagus5, BSCC-AdC also sometimes occurs in hypopharynx.6
Bicomponent cancer of SCC and ACC also should be concerned for the potential limitation of tissue biopsy. Unlike overlapping malignancy of head and neck SCC and esophageal SCC, collision tumor of head and neck was barely seen. But there was collision tumor of SCC and ACC in larynx or hypopharynx reported before, even with synchronous esophageal carcinoma like this case. 7,8 Complete histological investigation of a neoplasm and affection on multicomponent tumors are crucial in the successful diagnosis of a collision tumor.
To our knowledge, hypopharyngeal subsequent ACC following SCC is a rare tumor not previously described. Pathology is needed to make the correct diagnosis, and complete excision is currently the standard treatment approach. Our case demonstrates that clinicians should be aware of the possible ACC, even if a diagnosis of SCC was made before, because different therapy strategy and oncological follow-up planning need to be considered for these two tumor entities.