Seventeen well-characterized human lung cancer cell lines were examined for the 
presence of specific membrane receptors for epidermal growth factor (EGF) and 
nerve growth factor (NGF) as well as for the production of diffusible factors 
capable of stimulating soft agar growth. These cell lines represented all four 
major histological types of human lung cancer including small cell carcinoma of 
the lung (SCCL) and the three types of non-SCCL (epidermoid, large cell, and 
adenocarcinoma). The SCCL lines included three lines referred to as "converters" 
because they had lost SCCL morphological and biochemical properties during 
prolonged passage in vitro. Specific receptors for EGF and NGF were detected by 
measuring the binding of 125I-radiolabeled growth factor to the cell surface. 
These assays revealed that EGF receptors are found on five of six non-SCCL cell 
lines and are not found on any of the SCCL lines. In contract, NGF binding was 
detected at low levels on three of eight SCCL lines and on all three SCCL 
converters but was not observed for non-SCCL lines. Thus, SCCL and SCCL 
converter cell lines are distinguished from non-SCCL by the pattern of membrane 
receptors for EGF and NGF. Such differences may ultimately prove useful as 
biological markers for the different histological types of lung cancer. 
Moreover, the majority of SCCL cells and all of the non-SCCL cells tested were 
found to produce diffusible growth factors which can stimulate soft agar growth 
of nontransformed normal rat kidney fibroblasts. Although some correlation 
between soft agar growth factor production and the absence of EGF receptors may 
exist for SCCL cells, the production of transforming growth factors appears to 
be a general property of human lung cancer cells in vitro and is independent of 
EGF receptor expression.