Is this why dogs have sometimes detected it?

Scent of melanoma: New research may lead to early non-invasive detection and diagnosis

It's only tests in the lab so far, but still:

The researchers used an absorbent device to collect chemical compounds from air in closed containers containing the various types of cells. Then, gas chromatography-mass spectrometry techniques were used to analyze the compounds and identified different profiles of VOCs emitting from melanoma cells relative to normal cells.

Both the types and concentrations of chemicals were affected. Melanoma cells produced certain compounds not detected in VOCs from normal melanocytes and also more or less of other chemicals. Further, the different types of melanoma cells could be distinguished from one another.

Noting that translation of these results into the clinical diagnostic realm would require a reliable and portable sensor device, the researchers went on to examine VOCs from normal melanocytes and melanoma cells using a previously described nano-sensor.

Constructed of nano-sized carbon tubes coated with strands of DNA, the tiny sensors can be bioengineered to recognize a wide variety of targets, including specific odor molecules. The nano-sensor was able to distinguish differences in VOCs from normal and several different types of melanoma cells.