Isolated tumor cells in bone marrow predict reduced survival in node-negative non-small cell lung cancer

It recently became evident that isolated tumor cells undetectable by conventional tumor staging are frequently present in bone marrow of patients with apparently localized non-small cell lung cancer (NSCLC). The clinical relevance of this minimal hematogenous tumor cell dissemination is under vigorous debate.

For tumor cell detection in the bone marrow, we used monoclonal antibody CK2 against the epithelial intermediate filament protein cytokeratin 18. The influence of a positive bone marrow finding on clinical outcome was studied in 139 patients with NSCLC postoperatively staged as pT1-4, pN0-2, M0, and R0 after a median follow-up of 66 months (range 48 to 74 months).

Cytokeratin-18-positive cells in bone marrow were demonstrated in 83 (59.7%) patients at the time of primary surgery and in 6 of 12 representative patients analyzed twice 3 to 18 months after surgery. In patients without histopathological lymph node metastases (pN0; n = 66), the occurrence of 2 or more tumor cells in bone marrow at primary surgery was a strong and independent predictor for overall survival (p = 0.007) in univariate analysis. The multivariate analysis showed a 2.8 times increased risk for shorter survival in patients with disseminated tumor cells versus patients without such cells. Four of the 6 patients with a positive cytokeratin status after surgery developed a tumor recurrence 11 to 44 months after the operation, while none of the patients with a negative bone marrow at all time intervals showed a tumor relapse.

Minimal residual bone marrow involvement is an independent prognostic factor for overall survival in patients with node-negative NSCLC, which may help to identify patients in need of an adjuvant systemic therapy. The postoperative persistence or reappearance of tumor cells in bone marrow indicates that these are not only shed cells but rather represent true micrometastasis.