Positive immunostaining with MLuC1 of bone marrow aspirate predicts poor outcome in patients with small-cell lung cancer.

Background: Immunocytochemistry has been proven able to identify tumor cells in bone marrow aspirate (BMA) of patients with SCLC. However, few data exist about the clinical significance of the procedure.
Patients and Methods: 108 BMA taken from 60 patients were incubated with the MoAb MLuC1 (cluster 6) and stained by the APAAP (alkaline phosphatase-antialkaline phosphatase) method. The serum levels of LDH, TPA, NSE and CEA were also studied in relation to bone marrow involvement by means of discriminant analysis.
Results: Immunocytochemistry of the aspirate with MLuC1 detected positive cells in 23 patients (38%) (38 of 108 samples) vs. 13% of the conventional biopsies studied without MLuC1 (P < 0.001). With respect to bone marrow positivity, three groups of patients were identified: those with no positive cells in the aspirate and negative biopsy (group A); those with less than 10 positive cells in the aspirate and negative biopsy (group B); and those with more than 10 positive cells or clumps in the aspirate or positive biopsy (group C). Group C patients had poorer median survivals than those in the other two groups (5.5 vs. 11 months, respectively, P = 0.01). Discriminant analysis showed that the four serum markers were poor discriminators of the degree of bone marrow involvement, with only 55% of grouped cases being correctly classified.
Conclusions: These results show that detection of bone marrow involvement i) can be improved by the use of MLuC1 ii) is not predictable by conventional tumor markers, and iii) is related to poor outcome.