Introduction:
Colorectal cancer is one of the common cancers that have metastasis or the cancer spreadability to other organs like the liver, peritoneum, or even the lung tissues. This cancer can be touted to be one of the disseminated diseases in medical literature with its potential for cancer or neoplastic cells to spread to more unusual sites across the body. In recent medical research, oral pathology researchers have documented some rare cases of colorectal cancers spreading even to the parotid gland. The primary salivary glands, such as the parotid gland in the face, are the sites of metastasis for parotid gland cancer, which typically originates from other head and neck cancers.
According to oral pathologists and as stated in dental research studies, the highest proportion of parotid gland metastases or tumors are usually linked only to head, face, neck, scalp, and neck cancers and with most of these cancers arising from squamous cell carcinomas of head and neck region. Hence even though it may seem extremely thin a possibility that parotid gland metastasis would be occurring in colorectal cancers, certain cases have been recorded that signify the same.
Based on recent medical studies, around 20 percent of parotid gland tumors are typically associated with primary malignant tumors found exclusively in the head and neck region. However, like other rare tumors, parotid gland tumors or metastases originating from other multiorgan cancers can pose a significant threat to life due to their high propensity for spreading through lymphatic or hematogenous (blood) pathways. Nevertheless, a small percentage of these tumors, approximately 25 percent, are attributed to metastatic origins, although they are considered rare occurrences.
For instance, in metastatic malignancies of the head and neck, in certain squamous carcinomas or melanoma tumors, parotid gland metastasis would indeed be implicated. Medical research shows that metastasis from tumors originating from below the clavicle to the parotid gland is usually considered very rare.
What Are the Incidents of Colorectal Cancer Metastasis to Parotid Gland?
Metastases to the parotid gland, as of currently estimated global incidence rates stand at around 8.1 percent, as recorded in medicine in a series of 6,000 documented cases. However, a few numbers can be recorded where disseminated cancers such as colorectal cancer can involve primary sites like the parotid gland (which is a major salivary gland) from the head and neck region.
Colorectal cancer metastasizes through two means mainly the lymphatic spread of cancer cells or the hematogenous spread. The hematogenous spread usually involves the cancer cells spreading primarily to the liver, peritoneum, or lungs.
The three-year survival rate for advanced colorectal cancer is typically very low, indicating a poor prognosis for patients. According to oncologists, the presence of cancer cells capable of spreading to other organs often leads to a grim outlook for patients. Additionally, metastases to uncommon sites such as skeletal muscle, heart, and thyroid tissues usually occur in patients with widespread, uncontrolled cancer.
How to Detect Parotid Metastasis?
Typically, parotid tumors lead to facial or jaw swelling without causing pain. Additional symptoms may include numbness, burning, or pins-and-needles sensations in the face, loss of facial movement, difficulty swallowing, mouth asymmetry, a sore or lesion on the lump, and trismus (restricted mouth opening). In some cases, one side of the face may appear larger or smaller than the other side.
Histologically, the preferred diagnostic method for detecting parotid gland tumors is the fine needle aspiration cytology which is also highly recommended according to oral and maxillofacial surgeons. Upon observation of the parotid gland afflicted, characteristic irregular tumor patterns can be seen in the cells either in papillary, solid, or in glandular growth patterns.
Fine needle aspiration biopsy (FNAB) is considered the most reliable method for pathologists and surgeons to accurately diagnose specific malignancies, particularly when dealing with a neck mass or suspected malignancy in the cervical lymph nodes. In cases of disseminated tumors with metastatic potential, such as colorectal cancers, prompt surgical intervention is crucial to improve the patient's prognosis. The oral surgeon will plan definitive surgical management to detect cancers in the head and neck, or more commonly, in the parotid gland. In such cases, a core biopsy that is the FNAB would be the timely tissue diagnosis procedure needed for detecting a possible secondary malignancy in the orofacial regions. Further, a core biopsy procedure is always indicated as the gold standard diagnostic method over open biopsy.
Immunostaining can be further useful in detecting accurately primary tumors as well as their rare sites of metastases. The immune profile of colon adenocarcinomas through this method is CK 20-positive (cytokeratin 20), CEA-positive (carcinoembryonic antigen), and CK 7-negative markers. An Increase in the CK 7 expression would often be indicative that the patient has an extensive cancer spread or a poorer prognosis in the cases of all colorectal cancer patients.
How to Manage Parotid Metastasis?
In patients with very poor prognoses or extensive tumor spreads, palliative radiation needs to be an option for pain control and a Capecitabine-Irinotecan therapeutic regimen should be initiated as per expert opinions to prevent further disease progression in colorectal cancers.
In the rare and challenging cases where head and neck regions, such as the major salivary gland as the parotid gland metastasis occurs, surgical resection or total parotidectomy (removal of the parotid gland) and neck dissection that would be followed subsequently by chemotherapeutic and radiation therapy treatment would be deemed treatments or choice for ensuring longer survival rates in individuals afflicted.
Conclusion:
Multidisciplinary management between the oncologist and the oral and maxillofacial surgeon would be needed in both diagnosing and surgically managing and improving the survival rates of these afflicted cancer patients. In cases of parotid gland metastasis from colorectal cancers, clinical discomfort would be possible like difficulty in food consumption, and orofacial pain which should be managed by the dentist or the oral surgeon. Despite its rarity, diagnosing disseminated tumors can be quite challenging, and the spread of cancer from these tumors can lead to complications in survival rates even following surgery or metastasectomy (surgery to remove metastases) along with subsequent systemic treatment, which is the preferred treatment option.
