The spread of cancer from its primary location to distant sites to recur later (metastasis and recurrence) is the major cause of death among cancer patients. By the time metastasis is detected, clinicians can do very little to treat their patients as they do not often respond well to conventional therapy. The lung is the second most common site of breast cancer metastasis and has the worst outcomes. We now know that even though patients have their tumours surgically removed and receive chemotherapy, tumour cells can still leave the primary tumour early and cause secondary breast cancer to recur later.

We use mouse models of human cancers to understand how tumours manipulate the immune system to thrive and metastasize in the lung. For immunological studies such as this, it is imperative that we use a whole organism with a fully competent immune system, because immune cells regulate each other. To capture difficult-to-image events, we use chemical ‘clearing’ protocols which allow us to make lungs transparent and allow to image very large volume of tissues in three dimensions. We combine it with the staining of different target molecules with fluorescent probes (multiplex) to visualize complex interactions between immune and tumour cells in the lung.

The image presented here shows a three-dimensional view of multiphoton microscopy images. We aimed to visualize lung immune environment one week after the injection of fluorescent tumours cells (red). Can you see the single tumour hidden in blood vasculature (white)? Other colours are for nuclei (blue), bronchial epithelium (cyan), macrophages (pink), fibrillar collagen (purple) and some other Immune cells expressing the CX3CR1 receptor (green).