A rare case of an aggressive polymorphous adenocarcinoma of minor salivary gland in the retro-maxilla

Polymorphous adenocarcinoma (PAC) is a low-grade malignant tumour of minor salivary glands of the oral cavity, which rarely presents with invasive features. Low metastatic and excellent survival rates are some of its favorable features. A 36-year-old woman reported with swelling, pain, and mobility of teeth in the left upper inner cheek region. Contrast enhanced computed tomography (CECT) revealed a large, lobulated, heterogenous mass in the left retro-maxillary region with a few enlarged left cervical lymph nodes (levels IB and II). After surgery, the final histopathology report gave a definitive diagnosis of PAC with certain invasive characteristics - perineural invasion, infiltration into skeletal muscle, and depth of invasion of 10 mm, which recurred in a different location 1.5 years later. A few predictable features of PAC include incidence in elderly women, asymptomatic presentation, occurrence in the posterior hard of soft palate, very low incidence of nodal or distant metastases, perineural spread, skeletal muscle infiltration, and low rates of recurrence with good survival outcomes. However, in our case, the patient appeared to present with a relatively aggressive form of PAC, considering her young age, symptomatic presentation, uncommon anatomic location in the retro-maxilla, cervical nodal metastasis, perineural and skeletal muscle infiltration, and local recurrence within a short period. Although PAC is a low-grade tumour with excellent prognosis, it may occasionally present with invasive characteristics, and early diagnosis and prompt management with strict adherence to post-operative regimens and follow-up is of prime importance to prevent any untoward outcomes.