INTRODUCTION
A 66-year-old man presented to the clinic with a rapidly expanding nodule on his right forehead. Examination revealed a 2 cm soft subcutaneous nodule that was clinically consistent with an epidermal inclusion cyst. The patient elected to have the lesion removed and this was performed in the office using local anesthetic. During the procedure, the lesion was noted to be deeply infiltrating with no capsule. It was unusually difficult to find the margins of the lesion.The patient tolerated the procedure well and his post-operative course was unremarkable. Pathologic evaluation of the lesion demonstrated it to be a cutaneous carcinoma consistent with a poorly differentiated squamous cell, poorly differentiated carcinoma, an adnexal carcinoma including an eccrine carcinoma, or a metastatic carcinoma. Pathologic examination revealed a 0.15mm nerve encased by the tumor. The overall histologic appearance suggested that this lesion was metastatic.At low magnification, it is evident that the lesion is not attached to the epidermis and that it is infiltrating into the deep dermis and subcutaneous tissue (Figure 1). Higher magnification (20x) reveals confluent sheets of cells that have prominent nucleoli and pleomorphic nuclei (Figure 2). At 40x, it is obvious that the cells are malignant but there is a lack of defining characteristics that might identify the etiology of the tumor (Figure 3).The patient’s past medical history included type II diabetes, hypertension, and hyperlipidemia. He had a squamous cell carcinoma removed from his left forehead using Mohs surgery approximately one year prior to presentation. There was no obvious source for a cutaneous metastasis.As part of the workup, the patient had a full body FDG PET/ CT scan that showed uptake in the right forehead. There were no primary lesions nor other metastatic lesions noted. He underwent wide local resection of the lesion with 1.5 cm margins at a tertiary cancer center. The pathology from the resection revealed no connection to the overlying epidermis and was consistent with a metastatic lesion. The lesion was positive for CK8/18 and MCK and negative for EMA, Melan-A, and S100. Following this resection, he was treated with radiation therapy.The question of how best to approach this cutaneous tumor of undefined primary was discussed with several oncologists. In addition, a discussion of potential treatments was discussed with the patient and his family. Since it was not clear whether or not the lesion was a primary or metastatic carcinoma, a second thorough review of systems and medical history was performed. No obvious risk factors or history of carcinoma was elicited. An additional imaging work up was performed with CT and PET CT scans at the referral center.
DISCUSSION
Cutaneous tumors with unknown primary lesions are uncommon in dermatology with a relative incidence of “3% of patients with advanced cancer”.1 The question of how to evaluate these lesions is one that has few guidelines. The advent of immunostaining, PET CT scans, and MRI scans as well as newer types of genetic analysis including gene expression profiling make the workup more targeted than it has been in decades past. Identifying the exact origin and etiology of a tumor of unknown primary is critical because treatment of these tumors is no longer relegated to broadly aimed chemotherapy. Instead, the
