Eli Lilly, the US drugs giant famous for creating the anti-depressant Prozac, today announced it was buying Loxo Oncology, a company that is barely five years old, for $8bn.
The takeover comes days after US-based Bristol-Myers Squibb said it was buying biotech firm Celgene for $74bn.
What both deals have in common is that they represent two of the world's biggest drug companies bulking up their position in cancer.
A third major global player, UK-based GlaxoSmithKline, agreed last month to buy Tesaro, another cancer specialist, for $5.1bn.
This deal was particularly striking because, under its previous chief executive, Sir Andrew Witty, GSK had appeared to be scaling back its work in cancer, exchanging part of its oncology business for the consumer and vaccines business of Swiss rival Novartis.
Sir Andrew's successor, Emma Walmsley, has said she wants oncology to be one of four fields on which GSK's huge research and development arm focuses.
In a separate development today, AstraZeneca, the UK's second-largest drug maker, announced it had hired a new head of research and development for its oncology unit.
The company has a number of very promising oncology products on which it is working and oncology has, for some time now, been one of the most important therapy areas for it.
So why has there been so much merger and acquisition activity in the field of oncology?
There are a number of factors, the first of which is that devising treatments for cancer is notoriously expensive, so it pays to have real scale in the field.
This is particularly the case in the US, the world's most important healthcare market, where drug makers offering different drugs for the same types of cancer have been looking to sell such treatments in bundles as they negotiate drug prices with healthcare insurers and providers - something that has become especially important as America's healthcare insurers pay closer attention to the effectiveness of treatments.
The second factor is that oncology is assuming greater significance to pharmaceutical companies because of recent big breakthroughs in the field and particularly in biotech.
Cancer is caused by genetic mutations and so, as gene mapping technologies improve, so should our understanding of how to combat cancer via gene therapy.
As significant, if not more so, have been breakthroughs in immuno-oncology, where cancer is fought off by a patient's immune system.
These are huge advances that have the potential to fight cancer far more effectively than existing treatments such as chemotherapy, radiotherapy and tumour surgery.
Thirdly, and connected to this, is the sheer size and scale of the opportunity in oncology.
As cancer is the second largest cause of death globally, after heart disease and stroke, demand for cancer treatments will continue to rise.
The big drug makers are seeing demand for their oncology products growing more strongly outside their traditional core markets - the US and Europe - as Asian countries like China and India devote more spending to healthcare.
Fourthly, a number of major cancer treatments are due to lose their patent protection in coming years - meaning that they face a hit to sales as cheap copycat drugs are launched.
For example, Alimta, a lung cancer treatment that is Eli Lilly's third-biggest selling drug, is due to come off-patent by 2021.
Similarly, Opdivo, a cancer treatment which is Bristol-Myers Squibb's best-selling drug, loses patent protection in 2022.
So the drug giants need to replace the earnings streams they will lose from these blockbusters.
So-called biologic treatments also enjoy longer patent protection than traditional chemical drugs under the new trade deal struck late last year between the US, Canada and Mexico.
That potentially increases the profitability of cancer treatments on which the new biotech firms are working when they come to market.
And lastly, a factor not to be underestimated, is the extent to which the sector is coming under pressure to cut prices.
Donald Trump has been a strident critic of Big Pharma for its pricing - he attacked the sector again at the weekend - and there is evidence that, to ward off further regulatory pressure from the president, drug makers are pushing through lower price increases than they have done historically.
Healthcare analysts at JP Morgan, the investment bank, argue that, as it is forced to reduce its dependence on pricing for profits growth, Big Pharma is instead going to have to rely increasingly on innovation and new drugs.
Oncology, as a field in which there is strong growth in demand and in which research is seeing some rapid breakthroughs, is an obvious place to direct some of that money.
