About 6% of all PAs harbor malignancy, most often in the form of CXPA [6]. Interestingly, although CXPAs most often occur in the parotid gland, they occur in minor salivary glands with greater frequency than would be expected by the rate of PA occurrence [7]. CXPAs have a female predominance, and occur in patients who are, on average, about 12 years older than patients with PAs [7, 8]. The two classic clinical presentations of CXPA are (1) recent rapid growth in a longstanding tumor, and (2) multiple resections of a PA with eventual malignant transformation [1, 7]. Any salivary carcinoma type can arise in a PA, but high-grade adenocarcinoma NOS and salivary duct carcinoma are the most common [1, 7, 8]. Very often, the PA component is associated with zones of hyalinizing fibrosis [1, 7, 8]. CXPAs are sub-classified as noninvasive, minimally invasive, and invasive based on the extent of invasion by the carcinoma beyond the PA [1]. This distinction becomes very important for determining the patient’s prognosis and guiding appropriate therapy; while non-invasive and minimally invasive CXPAs only rarely behave in a malignant fashion [9], invasive CXPA has an overall 5-year survival of approximately 30% [10].

CXPA is regarded as the rarest of all malignancies of the sinonasal tract, to the extent that it has been called a “medical curiosity” [3]. There have been only three prior well-documented cases [2, 3]. An additional case by Chimona et al. [11] was reported as a nasal mucoepidermoid carcinoma ex-PA presenting in a male patient, but in this report there was insufficient photomicrographic evidence presented to support this diagnosis. Table 1 summarizes all the published cases of this entity in addition to our two cases. Although the number of total cases (5) is admittedly small, some interesting trends are notable. Like CXPA in general [7] but unlike benign PA of the nasal cavity [5], there is a female predominance of nasal CXPAs with all cases having presented in women. Like benign PA of the nose [5], most (4/5) cases of nasal CXPA involved the nasal septum and the most common clinical presentation was obstruction. The average age of the affected patients was 57.5 years, about 15 years older than the average age of patients with benign PA of the nasal cavity [5]. There was a slight predominance of right-sided lesions (3:2). Unfortunately there are too few cases with follow-up to make any meaningful conclusions about the clinical behavior of nasal CXPA and whether the WHO subclassification scheme (i.e. noninvasive, minimally invasive, or invasive) is useful in that setting.

The nasal CXPA cases differ from CXPAs as a whole in a few interesting ways. Not surprisingly, the most common presenting symptoms of CXPA in the nasal cavity were obstruction and epistaxis, but none of the affected patients had one of the “classic” clinical histories of CXPA (i.e., multiple recurrences or recent growth of a longstanding mass). Also, neither of our cases had the classic histologic feature of dense fibrosis or hyalinization in the PA component; this feature was described in only one of the other three previously published cases [2]. Although CXPAs are generally larger than benign PAs [7], the three cases where size was reported averaged 2.67 cm, essentially identical to the average size of benign PA of the nasal cavity (2.6 cm) [5]. Also, while benign PAs of the nasal cavity are often very cellular [5], the PA component of nasal CXPAs was dominated by a myxoid to chondro-myxoid stroma in four of the five cases [3]. Finally, it is interesting that adenoid cystic carcinoma, an uncommon malignancy to evolve from PAs in other sites, represents 40% of the reported cases of CXPA in the nasal cavity.