13.27 Primary site unknown after appropriate search for primary —metastatic carcinoma or sarcoma, except for solitary squamous cell carcinoma in the neck.

Except for a solitary squamous cell carcinoma found in the neck, any other metastatic carcinoma or sarcoma found in the body; and the primary site of origin of that tumor is unknown after a thorough metastatic work up, will meet this listing.

Under the revised listings, SSA evaluates tumors based on histology. For example, there is no histology for a “primary abdominal neoplasm.” Tumors that have spread to the abdomen should be evaluated under the site of origin, if known. If the primary site is unknown, SSA will use this listing to evaluate this or any similar impairment.