Invasive ductal carcinoma is the most invasive histological pattern of breast cancer. Distant spread through the lymphatic route occurs to the mediastinal and supraclavicular lymph nodes. Also hematogenous spread occurs and leads to metastasis to lung, liver, bone, adrenals, and brain [10
]. However, metastasis to the parotid gland is a very rare clinical event for breast cancer. In a review of autopsy studies which included 167 cases of breast cancer, only 1 case of metastasis to the parotid gland was detected [11
]. Also, a search of the MEDLINE database (1982–2010) revealed merely 14 cases (table ) [2
]. One reason for the rarity of this event is the anatomical location. Metastasis to the parotid gland usually arises from primaries in the head and neck. The parotid gland is divided into paraglandular lymph nodes, intraglandular lympatics, and parenchyma. The paraglandular and intraglandular lymphatics are common sites for metastasis from squamous cell carcinoma and melanoma of the scalp, ear, and the forehead by direct lymphatic drainage. On the other hand, parenchymal metastasis is considered to occur via hematogenous rather than lymphatic spread [12
]. However, few reports document which area in the parotid gland is affected by metastasis, and the metastatic process remains to be elucidated. To our knowledge, 11 of the 14 patients had left parotid gland metastasis (5 primary breast carcinomas in the left and 5 in the right breast; 1 case unknown), and 3 patients had metastasis to the right parotid gland (1 primary in the left and 2 in the right breast). Since 5 (45.5%) of the 11 patients with left parotid involvement had a primary carcinoma in the right breast, it is possible that the spread occurred via hematogenous as opposed to direct lymphatic metastasis.
Case reports of parotid gland metastasis of breast cancer
For the treatment of this metastasis, parotidectomy, radiation, chemotherapy, and hormone therapy were performed. Regardless of the metastatic pathway, generalized treatment such as chemo- and hormone therapy is needed. Because immunohistochemical analysis in our case had revealed the tumor to be negative for estrogen and progesterone receptors and positive for HER2, we continued to administer trastuzumab postoperatively. Trastuzumab combined with chemotherapy drugs such as paclitaxel improves outcomes among women with surgically removed HER2-positive breast cancer [14
]. It also improves disease-free survival if continued after adjuvant chemotherapy [15
]. However, the effect of postoperative adjuvant chemotherapy in stage IV breast cancer patients is controversial.
In spite of various treatments, in this case, the patient experienced a relapse 11 months after operation. At that time, there were some treatment options such as to continue or discontinue trastuzumab (change to lapatinib) and start or not start chemotherapy. Lapatinib, a tyrosine kinase inhibitor of HER2 and epidermal growth factor receptor, is an active combination with capecitabine in women with HER2-positive metastatic breast cancer that has progressed after trastuzumab-based therapy [16
]. We started capecitabine in addition to trastuzumab, which is one of the strategies applied in HER2-positive breast cancer, and this approach proved effective.
The case presented here had an unusual clinical course. Oncologists should keep in mind that the clinical course or imaging findings are not always in line with common patterns. Rare presentations such as in our case are possible, and we should always strive for a histopathologic diagnosis.