We were specifically interested in addressing the following questions: (i) can tissue clearing and fluorescence microscopy be used to measure tumour burden with sufficient sensitivity; (ii) what is the heterogeneity of TAM infiltration across metastatic lung tumours1; and (iii) what is the effect of PLX3397, a competitive ATP inhibitor with potent specificity for CSF-1R and cKIT receptor tyrosine kinases on macrophage density, cellular distribution and ultimate tumour progression; and (iv) can one measure nanotherapeutic delivery to individual tumour nodules? The gene discussed is NTRK1; the disease is neoplasm.