Salivary duct carcinoma is a cancer originating in the ducts of the salivary glands, located in and around the mouth and throat. This malignancy is uncommon and known for its aggressive behavior, meaning it has a tendency to grow and spread quickly. The disease is most frequently diagnosed in men over the age of 50.
A defining characteristic is its microscopic appearance, which closely resembles ductal carcinoma of the breast. This similarity helps distinguish it from other salivary gland cancers. A notable percentage of these cancers develop from a pre-existing benign lesion known as a pleomorphic adenoma.
Symptoms and Affected Locations
The most common initial sign of salivary duct carcinoma is the appearance of a firm lump or swelling. This mass often grows rapidly and can be located in the areas around the jaw, neck, or cheek. While some individuals may experience pain associated with the lump, it is not a universal symptom.
A more specific set of symptoms arises when the tumor affects nearby nerves, particularly the facial nerve. This can lead to facial weakness, numbness in parts of the face, or even paralysis on one side, a condition known as facial nerve palsy. The involvement of the facial nerve is considered a negative prognostic indicator.
The vast majority of cases (80-83%) originate in the parotid gland, the largest salivary gland located in front of the ears. The submandibular gland, found under the jawbone, is the second most common site, accounting for 8-12% of cases. It is much less common for this cancer to develop in the sublingual glands or minor salivary glands.
The Diagnostic Process
The diagnostic process begins with a clinical evaluation and physical examination. A doctor will assess any lumps or swelling and check for signs of nerve involvement. This is followed by advanced imaging like Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) to determine the tumor’s size, location, and if it has grown into adjacent tissues.
To confirm the presence of cancer, a tissue sample must be obtained through a biopsy. One common method is fine-needle aspiration (FNA), but a core needle biopsy, which removes a larger piece of tissue, may be needed for a more definitive analysis. A pathologist examines the tissue to confirm the diagnosis.
Further testing, known as immunohistochemistry (IHC), is performed to detect specific protein markers on the cancer cells. Testing for the Androgen Receptor (AR) and human epidermal growth factor receptor 2 (HER2) is standard, as their presence directly informs treatment strategies.
Treatment Modalities
The primary treatment for salivary duct carcinoma is surgery, with the objective of completely removing the tumor. Surgeons aim to achieve “negative margins,” meaning the tissue surrounding the tumor is free of cancer cells. Depending on the tumor’s location, this may involve a parotidectomy, the removal of the parotid gland, and a neck dissection to remove nearby lymph nodes.
Following surgery, patients often receive adjuvant radiation therapy. This treatment uses high-energy rays to target the surgical area, destroying any remaining cancer cells to lower the chance of local recurrence.
Systemic therapies, which treat the entire body, are selected based on the specific molecular markers found on the tumor cells.
- For tumors that test positive for the Androgen Receptor (AR), androgen deprivation therapy (ADT), a type of hormone therapy, may be used.
- If the cancer cells show an overexpression of the HER2 protein, targeted therapy with drugs like trastuzumab can be effective.
- Traditional chemotherapy is generally reserved for cases where the cancer is advanced or has spread to distant parts of the body.
- Chemotherapy is also used for tumors that do not have AR or HER2 markers.
Prognosis and Follow-Up Care
The long-term outlook for an individual with salivary duct carcinoma is influenced by several factors identified at diagnosis. The stage of the cancer, which indicates tumor size and spread, is a significant determinant. Other factors include whether the surgical margins were free of cancer cells and the extent of lymph node involvement.
The cancer carries a notable risk of recurrence and metastasis, which is the spread to other parts of the body like the lungs, bones, or brain. Given the potential for the cancer to return, follow-up care is a necessary part of management. This involves a regular schedule of appointments with the medical team for physical examinations to check for any signs of recurrence.
Routine imaging is also a standard component of the follow-up plan, and patients can expect to undergo periodic CT, MRI, or PET scans to detect any recurrence as early as possible. Recurrence is rare after five disease-free years.