Not to dismiss the risk, as I also have issues with deca and its negative cardiovascular effects, but it's about perspective.
As mentioned in the study itself, estradiol (a necessary hormone in the body) is also cytotoxic and genotoxic. As is tamoxifen, asparaginase (an enzyme used in normal food manufacture), and a whole load of other common drugs used in medicine (anti biotics, chemotherapy, anti virals etc). And in your other article it also points out that just regular petrol station attendants endure worse exposure.
Millions of 'cancers' form inside our bodies every day, most of us will never know because our immune systems destroy them just as quickly. Who knows at what point a few genetic misreplications finally produce a cancerous cell that becomes a tumour? All kinds of activities, substances and lifestyles over a number of decades can affect that risk. But in the grand scheme of things, using Deca a few times a year will probably have no impact whatsoever.
PS props to Ergo log, I love their website.