Mindfulness has been applied in many clinical therapies, mindfulness-based stress reduction, mindfulness-based cognitive therapy, acceptance and commitment therapy, and so forth. For me mindfulness means being present in the now. Breast cancer is a crisis where the best help comes from a peer group, from those who undergo or underwent the same type of crisis.  You have to confront your state of being mortal, something people normally repress because their subconciousness lives for ever. Behavioral activity just distracts the patient from the real issue. A woman who undervent surgery for a small malign lump tells her story:  She was placed after the surgery in a ward between women suffering from the same. It happened so that on one side was a women with both breasts removed and on the other side was the daugther of a funeral director. 3 more women were in the room The daugther of the funeral director took the ladies through the whole funeral process during the hours of the night with comments like "bad peoples get oak coffins with soft velvet while nice people get simpler "clothing" for the last trip" (it had to do with feelings of guilt in close ones). The night hours were frank, therapeutic and a good experience for the ladies to come to terms with the state of being mortal. 

I think it depends of the level of anxiety and depression that the person is suffering. In my experience, mindfulness helps to decrease symptoms in patients and increase their perception of quality of life.

There is no easy answer to your question. It really depends on the patient's individual situation. Mindfulness based approaches are clearly helpful in many cases, as is behavioral activation, provided the patient is a stage when they can still be behaviorally  activated. There are, of course, many other elements that may be applied, such as cognitive restructuring, and, maybe more importantly, dignity therapy, with or without including the patient's relatives. Finally, in psychooncology, the "longer term impact" may not be of highest importance because some patients' perspectives regarding survival are less than long term.

When you are in a life-threatning situation anxiety and depression are normal responses to the situation, not necessarily conditions that shall be deleted. These unpleasant feelings help us grow and mature as human beings so that we can die with some dignity left. We know based on our research that the best "medicine" in many cases is a strong social network. Cancer has had such a bad reputation that the poor patient has to be the strong one and comfort the close ones. In case no social network, no partner support, is available, peer support groups with persons who successfully resolved this kind of crises are the most effective helpers. After all, half of the global population never had any breasts.

I think the appropriate is depend on stage of cancer and also depend on individual cancer patient. It also depend on what kind of cancer they got. We need assess patient first and then decide what kind of treatment we apply for

In many of the studies that have used this approaches, their non-metastatic patients and in the active stage of the disease have been. The results also indicate the usefulness of both methods. I agree with Ulrich Schnyder opinion ,but a more appropriate approach for these diseases will be presented.

Let me refer you to:  www.copingengine.com. It's an interactive website that allows the user to identify their negative feelings, negative coping, (yes 'we' contribute to our anxiety and depression with our unhelpful coping techniques like 'blaming,' and then moves the user to choose one of many active coping choices that can move them towards a happier outcome... Behavioral approaches help with self recognition, and choosing new adaptive choices....

This was fun! However, in the moment when you face the crisis going to the computer and doing this would hardly help. In that moment a person of deep understanding is needed.

Funny that you think that a man - who most likely did not undergo this experience - is the most qualified to answer the question. I answered you based on personal experience.