Morphologic Findings in PET-Positive, Tumor-Negative Lymph Nodes in Patients with Lung Cancer
DR Semmel, B Daly, CJ O'Hara. Boston Medical Center and Boston University School of Medicine, Boston, MA
Background: Positron Emission Tomography (PET) imaging has become a major preoperative tool used to assess lung cancer tumor burden in lung and extra-pulmonary sites, including lymph nodes. Not infrequently, PET scans exhibit positive FDG uptake in lymph nodes, indicating presumed nodal metastasis, which subsequently reveal no detectable tumor on routine histological evaluation. As little is known about the histology of these nodes, the goal of this study was to look at the morphologic characteristics of PET-Positive, Tumor-Negative (PPTN) lymph nodes and compare them to PET-Negative, Tumor-Negative (PNTN) nodes from similar sites.
Design: In total, 68 blocks of PPTN lymph nodes from 15 patients and 16 blocks of PNTN lymph nodes from 7 patients with known primary non-small cell lung cancer were evaluated for the following histologic parameters: Histiocytosis (SH), Anthracosis (AN) and Follicular Hyperplasia (FH). In addition immunohistochemical stains for cytokeratins (AE1/3) were included to detect possible missed metastasis and stains for Ki-67 to assess cellular proliferation.
Results: The most significant findings were morphologic and are summarized in the following table:
Sinus Histiocytosis (SH) and Anthracosis (AN)SH: 0=none, 1=sinus expansion, 2=histiocytosis w/ aggregates, 3=sheetlike aggregates/granulomas. AN: 0=none, 1=mild, 2=moderate, 3=severe
Follicular Hyperplasia0=none, 1=rare atrophic follicles, 2=prominent follicle formation
The most notable morphologic findings in the PPTN nodes were increased sinus histiocytosis and anthracosis. Well-formed granulomas were noted in 3 patients. Missed micrometastases (< 1mm) were observed in only two patients. Ki-67 staining (range from <5 to 15%) was found mostly in secondary follicles when present and was negligible in the histiocytic component.
Conclusions: The major histological correlate for the increased FDG uptake in PPTN nodes is sinus histiocytosis and anthracosis. The increased uptake appears not to be due to an increased proliferative activity of these cells. Nodal follicular hyperplasia, micrometastasis and granulomas are less of a factor.
Monday, March 9, 2009 1:00 PM
Poster Session II # 221, Monday Afternoon