Background: Surgical removal remains the principal treatment modality in the management of lung cancer. Our aim is to characterize the effects of tumor removal on subsequent tumor recurrence at both local and systemic levels.
Methods: C57/BL6 mice [10/group] underwent a mammary fat pad inoculation of 3LL cells [5 x 10(5)/animal] and were divided into two groups. Group 1 served as control while mice in group 2 were further subdivided into groups 2A and 2B. After 2 weeks, all mice in 2A were killed, and primary tumors and lungs were excised. At 2 weeks, primary tumors were excised completely for all mice in group 2B. These mice were then recovered and recurrent tumor growth evaluated for a further 2 weeks. Four weeks from the onset of the study, all remaining primary tumors and lungs were excised from groups 1 and 2.
Results: After 4 weeks undisturbed growth, primary tumors in group 1 reached a mean size of 2.85 +/- 0.33 cm. After 2 weeks growth, primary tumors in groups 2A and 2B were comparable at 1.36 +/- 0.44 m and 1.53 +/- 0.29 cm, respectively. Two weeks after primary tumor excision, recurrent tumors in group 2B had reached a mean size of 2.65 +/- 0.74 cm. Moreover, for several animals, recurrent tumors rapidly reached similar volumes to that of primary tumors in group 1. Primary tumors were typically encapsulated and nonadherent. In contrast, recurrent tumors were locally invasive and adherent to chest wall and wound. Interestingly, pulmonary metastatic burden was increased in group 2B relative to group 1. Histologic examination revealed increased mitosis in recurrent tumors when compared with primary tumors.
Conclusions: Tumor removal is followed by accelerated growth of locally recurrent tumors and metastases. Moreover, recurrent tumors are more locally invasive than primary tumors. These findings strongly indicate that resection may be followed by tumor progression in residual disease.