Salivary Gland Tumors
Pathology
- Mucoepidermoid Carcinoma: low grade, slow-growing, well-curcumscribed. Curable by surgery alone. High grade mucoepidermoid can be invasive with increased lymphatic spred potential. Most common cancer of the partoid gland.
- adenocarcinomas are high grade associated usually with minor salivary gland tumors of the OC. There is a posensity for PNI, 30% for lymph nodes metastasis and distant spread in high grade lesions.
- Malignant mixed tumors: arise from benign mixed tumors such as pleomorphic adenoma. Carcinosarcomas contain both epithelial and mesenchymal components. Aggressive and associated iwht increased risk of local recurrence s/p surgery with a high propensity for lymph node metastasis.
- Carcinoma ex Pleomorphic Adenoma: arise from pre-existing benign adenomas having only epithelial origins. Most aggressive salivary gland histology with lymph node involvment in 20%. LN involvement is the most important survival determinant.
- Adenoid Cystic Carcinoma: Predominant in submandibular and minor salivary gland tumors. Recurrences can happen at any time, even 20 years or more. Lymphon node spread is uncommon. Perineural spread is common tracking to the base of the skull along cranial nerves. 40% will develop pulmonary metastases. Primary site must be managed adequately despite pulmonary mets due to long survival (10-20 years).
- Acinar Carcinoma: second most common malignancy of the parotid gland. Low grade, slow growing. Can be locally invasive and have a high risk for local recurrence (30-40%). Lymph node mets are low (< 20%) Distant mets < 20%. Later recurrences can develop many years after initial treatment.
- Salivary Duct Carcinoma: Rare, aggressive. 27% aries from pre-existing ploemorphic adenoma. Propensity for involving parotid, Increased risk for PNI and LN mets of 73%. Distant mets is most common cause of failure. Poor prognosis.
- Squamous Cell Carcinoma: Rare, very aggressive tumors. Local invasion of adjacent structures is typical. Lymph node mets are 50-60%. I parotid gland is involved, look for a primary site or lesion or mets to the parotid from an adjacent primary skin site.
- Undifferentiated: very aggresive with 30% from pre-existing pleomorphic adenomas. Very high risk of LN mets (50%).
Parotid gland parenchyma or lymph nodes may be involved by metastatic spread from another primary site, most frequently primary skin cancers of the scalp, face and ears. Hematologic spread can occur from primary lung cancers and less frequently, breast, kidney and GI. Prognosis is poor with mets to the parotid region from another primary site.
Clinical Presentation and Diagnostic Workup
Examine for masses, trismus (involvement of the pterygoids), EAC, are required. Functional status of CN VII (Bell's), and for deep lobe involvement IX, X, XI, XII. CT/MRI can be helpful. Imaging from teh base of skull, parotid RP, Cervical and supraclavicular LN is important. Pretreatment imaging is indicated in deep lobe parotid tumors, neurological symptoms, recurrences and alrge tumors.
PET scans are not particularly useful except in high grade tumors after diagnosis as part of a metastatic work up where another primary is suspect. Only 20-25% of parotid masses are malignant. Some surgeons believe FNA aspirate would not change their managment and prefer a parotidectomy. Incisional or excisional biopsies are never perfomed for tissue diagnosis because of the increased likelihood of recurrence. There is risk of injury to the 7th CN. Regional lymph nodes must be carefully evaluated due to the overall risk of lymph node involvement in the range of 17%
Treatment
Surgery
En bloc resections of the entire superficial lobe for superficial lobe lesions (90%) is the current standard. Excisional biopsies alone are not done because it violates the surgical field and is associated with a high recurrence rate. If the tumor is adjacent to the deep lobe, it may be necessary to take both the deep and superficial lobes. With locally advanced disease involving the adjacent soft tissues of skin, muscle or bone, a large en bloc resection may be required (radiacla paotidectomy). Radiation can begin post-operatively in 3-4 weeks provided there is good wound healing, even when a nerve graft or cable re-approximation is performed. Functional outcomes of nerve grafts are variable. Nerve injry in total parotidectomy affects the CN 7 and closure of the I/L upper eyelid. A gold weight in the upper eyelid is used to correct this with intent to prevent corneal exposure and ultimately, blindness.
Radiation Therapy
Indications for treatment: medically or surgically unresectable primary or previously unirradiated recurrent malignant salviary gland tumors can be treated iwth EBRT (low LET) usnig ocnventionla or altered fractionation or brachytherapy with/without EBRT or neutrons.
Indications for post-operative Radiation therapy:
- Resectable T3-T4 primary lesions and recurrent turmos
- Gross residual disease
- Close/microscopically positive marings
- Deep lobe parotid tumors
- PNI/LVI
- High grade histology
- Adenoid cystic
- Loco-regional LN mets.
- surgical concern of resection margins or turmor spilage, less than en bloc resection.t