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Polymorphus adenocarcinoma (PAC)

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Polymorphous adenocarcinoma

Polymorphous adenocarcinoma (PAC) is a rare type of salivary gland cancer that accounts for around 12% of malignant salivary gland tumours [1]. It is typically slow-growing and less likely to spread than some other salivary gland cancers. Most people diagnosed with PAC have a good outlook, especially when it is caught early and treated appropriately [2, 3].

Polymorphous adenocarcinoma usually begins in the minor salivary glands, which are the small glands found throughout the lining of the mouth and throat. The most common site is the roof of the mouth (the hard palate), but it can also occur in other areas such as:

  • The inside of the cheeks
  • The tongue
  • The lips
  • The floor of the mouth

It is very rare in the major salivary glands (parotid, submandibular, and sublingual) [2, 4].

PAC most often affects adults aged 40–70 and is slightly more common in women than in men. Because it grows slowly and often causes few symptoms early on, it may go unnoticed for some time [3, 4].

Many cases of PAC are now known to be associated with alterations in the PRKD1 gene. This finding may help improve diagnosis and eventually lead to more targeted treatments, although this is still an area of ongoing research [5, 6].

The symptoms of PAC can vary depending on where the tumour is located. Some people may notice:

  • A painless lump or swelling in the roof of the mouth or another area of the mouth
  • Difficulty speaking or swallowing (if the tumour is larger)
  • Occasionally, ulceration or bleeding [2, 4]

Because this cancer usually grows slowly, these symptoms may develop gradually over time.

Diagnosis

Diagnosis typically involves:

  • A clinical examination by a specialist
  • Imaging scans (such as MRI or CT) to assess the size and location of the tumour
  • A biopsy, where a small sample of the tumour is taken and examined under a microscope [7]

The cancer cells in polymorphous adenocarcinoma tend to look quite similar to each other under the microscope (this is called ‘uniform cytology’). But the patterns they form can vary a lot, showing different shapes and arrangements (this is called ‘architectural diversity’). Sometimes further tests (such as molecular testing) are needed. [2, 7]

Treatment

The main treatment for polymorphous adenocarcinoma is surgery to remove the tumour. If the tumour is small and well-defined, surgery may be curative on its own. In some cases, additional treatment may be recommended, including:

  • Radiotherapy – This may be used after surgery if there is concern about incomplete removal, if the tumour shows signs of more aggressive behaviour, or if there is involvement of nearby tissues.
  • Follow-up monitoring – Regular check-ups are important to detect any recurrence, especially as this cancer can sometimes return after treatment, even years later [2, 4, 8]

Chemotherapy is not usually used for polymorphous adenocarcinoma, as it tends not to respond well to standard chemotherapy drugs. However, research is ongoing into better treatments, especially for rare cases where the cancer spreads or comes back [4, 8].

Polymorphous adenocarcinoma is usually a low-grade cancer, which means it grows slowly and is less likely to spread than other types. Most people treated for PAC have a very good prognosis, particularly if the tumour is caught early and fully removed [3, 4, 8].

However, in rare cases, PAC can recur or spread to nearby lymph nodes or tissues. Long-term follow-up is important [2, 4].

References

  1. Alsanie I, Shah KA, Adkins DR, et al. Distribution and Frequency of Salivary Gland Tumours: An International Multicenter Study. Head Neck Pathol. 2022;16(4):1043–1054.
  2. Barnes L, Eveson JW, Reichart P, Sidransky D. World Health Organization Classification of Tumours. Pathology and Genetics of Head and Neck Tumours. Lyon: IARC Press; 2005.
  3. Jayaram N, Jayaram HN, Sundaram C. Polymorphous low-grade adenocarcinoma of the salivary glands: a systematic review. Eur Arch Otorhinolaryngol. 2020;277(3):819–826.
  4. Seethala RR. An Update on Grading of Salivary Gland Carcinomas. Head Neck Pathol. 2009;3(1):69–77.
  5. Weinreb I, Piscuoglio S, Martelotto LG, et al. Hotspot PRKD1 E710D mutation characterizes polymorphous low-grade adenocarcinoma of the salivary glands. Nat Genet. 2014;46(11):1166–1169.
  6. O’Sullivan-Mejia J, Xu B, Katabi N. PRKD1 gene rearrangements and mutations in polymorphous adenocarcinoma: diagnostic and clinical implications. J Oral Pathol Med. 2021;50(7):648–655.
  7. Bell D, El-Naggar AK. Molecular heterogeneity in low-grade salivary gland carcinomas: clinical implications. Curr Oncol Rep. 2016;18(3):17.
  8. National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Head and Neck Cancers, Version 2.2024. Plymouth Meeting, PA: NCCN; 2024.

Useful resources

Read more about how to get your tumour profiled and add to the research biobank at the Christie Hospital in Manchester, UK here:

Last updated May 2025