Metastatic Melanoma to a Single Nodal Site
Approximately 5% of patients with malignant melanoma will present without a documented primary site. Special stains and electron microscopy may be important in establishing the diagnosis. Patients with this diagnosis should, like those with stage II melanoma, have a radical lymph node dissection. Survival is actually slightly better than that seen in patients with stage II melanoma with a documented primary site.[5,17,18,19] (Refer to the PDQ summary on Melanoma Treatment for more information.)
Isolated Axillary Metastasis
Most patients who present with nodal metastasis above the diaphragm ultimately are documented to have lung cancer, the most common supradiaphragmatic primary malignancy. The presence of isolated axillary metastasis in females, however, raises another possibility. A few studies involving a small number of patients have shown that approximately 50% of patients who present with isolated axillary metastasis of an adenocarcinoma will ultimately be shown to have breast cancer. Although some of these patients will have a positive mammogram after the initial evaluation, approximately 50% of the patients will not. When these patients are treated with local excision, or as having primary breast cancer, 2- to 10-year survival has been obtained in approximately 50% of patients. The availability of estrogen-receptor (ER) and progesterone-receptor (PR) assays may aid in this diagnosis, and these studies should be performed in this setting. If the clinical setting is consistent with breast cancer, and ER and/or PR levels are elevated, CUP with this distribution should be treated as breast cancer.[1,4,20] (Refer to the PDQ summary on Breast Cancer Treatment for more information.)
Inguinal Node Metastasis
Squamous carcinoma detected in the inguinal lymph nodes is almost always metastatic from the genital or anal/rectal area. In females, careful examination of the vulva, vagina, and cervix is indicated, with biopsy of any suspicious areas. The penis of uncircumcised males should be carefully inspected. In both sexes, the anorectal area should be carefully examined, including biopsy of suspicious areas. Isolated metastases present in the central nervous system, the liver, and the genitourinary tract. Information about these presentations may be found in PDQ summaries that specifically detail their management.
In addition to the above situations, significant palliation can be achieved in certain instances in patients with CUP. Breast, prostate, ovarian, and thyroid cancers are all treatable malignancies, even when metastatic, and they represent approximately 15% of all CUP tumors. As with other CUP presentations, the pattern of spread of these malignancies is somewhat atypical. For instance, patients with prostate cancer who present with CUP have an inordinately high incidence of metastases to nonosseous sites such as lung (75%), liver (50%), and brain (25%). Bone metastases are also less common than lung metastases in thyroid cancer presenting as CUP.
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