From the Guidelines
Adenoid cystic carcinoma of the salivary glands most commonly metastasizes to the lungs, which is the site of distant metastasis in up to 90% of cases, followed by bones, liver, and brain. The lungs are the primary site of metastatic involvement beyond the head and neck, as reported in a study published in the Journal of the American College of Radiology in 2023 1. This study highlights the importance of surveillance imaging or follow-up imaging for suspected or known recurrence, especially since perineural tumor spread is common in adenoid cystic carcinoma.
Some key points to consider about the metastasis of adenoid cystic carcinoma include:
- The majority of recurrences, approximately 70%, occur in the first 3 years following treatment, and can be subclassified into local, regional, and distant 1.
- Distant metastases are documented in 33% of patients, with adenoid cystic carcinoma being one of the most common types to metastasize 1.
- The most common sites of metastatic involvement, in order of frequency, are the lungs, bones, liver, and brain, with the lungs being the most frequent site in up to 90% of cases 1.
- Bone metastases typically affect the spine, ribs, and pelvis, while liver involvement occurs less frequently than lung metastases.
- Brain metastases, though less common, can develop particularly in advanced cases, emphasizing the need for long-term surveillance for recurrence and metastatic disease.
Given the high frequency of lung metastasis, regular follow-up and surveillance imaging are crucial for early detection and management of metastatic disease, particularly in patients with adenoid cystic carcinoma of the salivary glands, as delayed diagnosis of tumor recurrence can portend a poor prognosis and decrease long-term survival 1.
From the Research
Common Areas of Metastasis
The common areas of metastasis for adenoid cystic carcinoma of the salivary glands include:
- Lung: The lung is the most frequent site of distant metastasis, with studies indicating that it is involved in approximately 42.8% to 54.9% of cases with distant metastases 2, 3.
- Bone: Bone metastases are also common, although less frequent than lung metastases, and are often found in combination with lung metastases 2, 3.
- Brain: The brain is another site of metastasis, although less common than the lung and bone 2, 3.
- Liver: Liver metastases can occur, particularly in cases of non-parotid adenoid cystic carcinoma, and may be related to local recurrence or metastases to other organs 2.
Patterns of Metastasis
The pattern of metastasis can vary, with some studies indicating that:
- Distant metastases can occur despite local control at the primary site, with a more fulminant course and shorter survival 4.
- The cribriform subtype of adenoid cystic carcinoma is associated with multiple local recurrences, greater local aggressiveness, and a poorer salvage rate, as well as late onset of local recurrences and distant metastases 4.
- The solid subtype has the worst overall prognosis in terms of distant metastases and survival 4.
Emerging Treatments and Genomic Landscape
Recent studies have highlighted the importance of understanding the genomic landscape of adenoid cystic carcinoma, with distinct molecular subtypes (ACC-I and ACC-II) associated with different disease biologies and treatment responses 5. Emerging treatments, including targeted therapies, are being developed and tested in clinical trials, with patient selection based on tumor molecular profile representing a major advance in the field 5.