FALSE TUMOR-POSITIVE LYMPH-NODES IN RADIOIMMUNODIAGNOSIS AND RADIOIMMUNOGUIDED SURGERY - ETIOLOGIC MECHANISMS

We investigated the causes of false-positive (nontumor cell) focal upt ake in radioimmunodiagnosis (RAID) and false-positive high counts in r adioimmunoguided surgery (RIGS). Tissue blocks of two such RAID cases were recut and examined by immunohistochemistry (IH) (group 1). Lymph nodes in the drainage area of 14 colon cancers selected because of tum or-positive draining nodes were examined similarly (group 2). The lymp h nodes in group 1 showed nontumor cell germinal center (GC) and rare macrophage (M phi) positivity with monoclonal antibody (mAb) CC49 to t umor antigen (Ag) TAG-72, the same Ag to which the mAb B72.3, used for the RAID studies, was directed. In group 2, CC49 staining was observe d in the colon cancers, in noncellular tumor Ag in lymphatic channels, and in the GC of draining nodes in a pattern similar to that of folli cular dendritic cells (FDC). An In-111-mAb/tumor Ag (TAG-72 or CEA) co mplex can result in false-positive RAID/RIGS studies by In-ill retaine d in the lysosomes of lymph node M phi, following attachment of the mA b to the Ag, and their catabolism in the M phi. An I-125-mAb to either tumor Ag could lead to false-positive RIGS studies due to its attachm ent to the Ag portion of ag/ab complexes affixed to the FDC in the GC of the lymph nodes draining a tumor. (C) 1996 Wiley-Liss, Inc.