ABSTRACT
Sinonasal cancer accounts for roughly only 3% of upper respiratory tract malignancies and generally presents as a primary malignancy. Although extremely rare, the sinonasal cavity is also a known location for metastasis, with 8% of these cases originating from primary breast cancer. When attempting to differentiate primary disease from metastasis, immunohistochemical analyses play a crucial role in reaching the correct diagnosis. To date, there are a handful of reports describing metastasis involving the paranasal sinuses but even fewer reporting primary sinonasal cancer with coexisting primary malignancy. Here we present a case of primary sinonasal adenocarcinoma in the setting of a long-standing history of breast cancer. The patient, a 73-year-old female, was diagnosed with T1cN1aM0, progesterone receptor positive and estrogen receptor negative ductal carcinoma in situ of the left breast in November 2019. She subsequently underwent bilateral mastectomy and treated with 3 cycles of chemotherapy and anastrozole, which were both discontinued due to intolerance. Of note, in March 2019, MRI of the head incidentally found a 3 x 2 cm mass in right nasal cavity extending into ethmoid sinus. One year later, she presented with mild right sided nasal obstruction and drainage, and biopsy revealed squamous and respiratory mucosa with chronic inflammation. The patient elected to cancel initial surgical resection of the mass due to the COVID-19 pandemic. The patient returned in March 2022 with complaints of eye pressure, double vision, headaches, and worsening nasal obstruction. PET/CT scan was negative for distant metastasis but demonstrated increased uptake in sinus cavity. MRI showed a larger 5 x 3.7 cm mass impressing on medial inferior margins of orbit. Imaging also suggested evidence of dehiscence of lamina and irregular neo-osteogenesis of the skull base. She underwent approach and resection of the mass with histology demonstrating a well differentiated, low grade non-intestinal mucinous adenocarcinoma. Immunohistochemistry was positive for pankeratin and CK7, favoring a primary sinonasal origin. It was estrogen receptor negative and negative for GATA3, a sensitive and fairly specific stain in mammary carcinoma. Adjuvant radiation was recommended postoperatively, however the patient declined this therapy. This case highlights the role of immunohistochemistry to discriminate a new primary cancer from metastasis in patients with a history of breast cancer. Clinically, patients with sinonasal metastasis can present with symptoms ranging from unilateral nasal obstruction, facial pain, diplopia, and decreased vision. On imaging, suspicion of malignancy is raised when there is evidence of destruction of bony boundaries and invasion of surrounding tissues such as the orbit and anterior skull base, as found in our patient. Notably, metastasis to the paranasal sinuses can mimic a primary cancer of the nasal cavity, with both tumors showing epithelial differentiation. However, primary tumors often show neoplastic changes in the overlying respiratory epithelium and do not express estrogen receptor, progesterone receptor, or HER2 positivity, which are known to be correlated with breast cancer. In this setting, GATA3 and estrogen receptor negativity allowed us to diagnose primary nasal cancer more confidently. Therefore, clinicians should be aware of metastatic disease and expand immunohistochemistry panels when appropriate.