It’s no surprise there’s a paucity of data for primary salivary gland cancers — they comprise only about 5% of all head and neck cancers, with roughly 2500 cases per year.¹ The standard of care as it stands is surgical resection for all. The extent of surgery is a topic of debate itself (and recently discussed at the 2024 Multidisciplinary Head and Neck Cancers Symposium in Phoenix, Arizona), especially for younger patients who have intact facial nerves. Further compounding this issue is the wide risk range of occult nodal metastases, being anywhere from 0% to 30%.

More questions arise when it comes to postoperative radiation therapy (PORT). Part of the conundrum revolves around the various histologic subtypes: Is it a recurrent benign pleomorphic adenoma? Or has it become a carcinoma ex pleomorphic adenoma? Maybe it’s a mucoepidermoid carcinoma that can easily be cured with surgery if it’s low grade but will readily metastasize if high grade. And if it’s an adenoid cystic carcinoma, every resident is ingrained with the knowledge that you have to chase the nerves back to the base of skull.

As medicine evolves through enhanced molecular testing and genomic knowledge, we must continue to dance around treatment standards, opportunities for de-escalation, and novel approaches, with the delicate balance of toxicity and efficacy for our patients at the forefront.

We have figured out that all adenoid cystic carcinomas require adjuvant radiation, given the highest rates of perineural invasion and common local recurrence, on top of a 30% to 40% rate of lung metastases in all comers.² For other histologies, PORT is recommended for any grade 3, positive surgical margin, perineural invasion, node positive, lymphovascular space invasion, and T3 or T4 disease — which is ultimately just an extrapolation from other head and neck cancers given the data void.

However, unlike other head and neck cancers, chemoradiation really isn’t in the cards for salivary tumors. Systemic therapy isn’t even mentioned in the NCCN guidelines until after consideration of adjuvant radiation and, even then, it is category 2B. But in a world where immunotherapy is trying to make its stand as the fourth pillar of oncology, one wonders how it might fit into the treatment paradigm. Especially given that recurrence and distant metastases are common, and with ASCO guidelines recommending lifelong monitoring,³ it seems that better systemic therapy is necessary. As medicine evolves through enhanced molecular testing and genomic knowledge, we must continue to dance around treatment standards, opportunities for de-escalation, and novel approaches, with the delicate balance of toxicity and efficacy for our patients at the forefront.

References

1. Alvi S, Chudek D, Limaiem F. Parotid Cancer. StatPearls. May 19, 2023. Accessed March 7, 2024. https://www.ncbi.nlm.nih.gov/books/NBK538340/
2. Lee RH, Wai KC, Chan JW, Ha PK, Kang H. Approaches to the management of metastatic adenoid cystic carcinoma. Cancers (Basel). 2022;14(22). doi:10.3390/cancers14225698
3. Geiger JL, Ismaila N, Beadle B, et al. Management of salivary gland malignancy: ASCO guideline. J Clin Oncol. 2021;39(17). doi:10.1200/JCO.21.00449