Does personality affect your outcome if you get cancer?

No, it doesn't.

There is a widespread belief in our society that people get, or, fail to recover from, cancer because of unresolved psychological issues or faulty approaches to handling thoughts and emotions.
Extensive research has shown no relationship between personality and likelihood of getting or recovering from cancer. But there is some contradictory research on the broader topic of emotions and illness:

1. Having a mental illness, like depression or anxiety, has been associated with increased physical illness and earlier death in a number of studies
2. Having 'trait positive affect' i.e. having a tendency to experience a lot of 'positive' emotions in your life - like joy, happiness, enthusiasm - is associated with longer life in some populations (e.g. community based older people) but not in others (e.g. people who were 'gifted' as children and had high levels of positive emotion were actually more likely to die before 65 than less happy gifted children)
3. Minimization of emotions has been found to be associated with longer survival in breast cancer patients but denial is associated with shorter survival.  The differences between these two approaches are important but subtle.
4. Emotions seem to pay a larger role in illnesses where inflammation is an important factor (e.g Heart Attacks, Diabetes, Infections) than in illness where inflammation isn't central (e.g.many cancers)
5. Research findings about one subset of an illness are sometimes different to another subset e.g. 'In breast cancer patients with a hormone (estrogen and/or progesterone) receptor positive status (biological factor), life events were related to recurrence of breast cancer, while such a relationship did not occur in women with hormone receptor negative breast cancer.' 
6. Some factors e.g.depression, perceived social support, anger/hostility, denial/avoidance) have shown both positive and negative relationships with survival from breast cancer.

So what are we to do in response to all this contradiction and uncertainty?  Here is my advice (for what it is worth!)

1. There is a consistent finding that social support is associated with emotional and physical health - so put effort into broadening and building important relationships.
2. Get clear about what a rich and meaningful life looks like to you and who you want to be in the world. Then behave in ways that move you towards living that life in each moment.  If you do develop a serious illness (we all will some day) you can look back on a life well-lived.
3. If you have a loved one with a serious illness and feel an urge to tell them how they should be handling their emotions
• Accept that different people have different ways of coping with challenges - something that works for you may not be right for them.
• Know that the messages our society gives about how 'unresolved psychological issues' cause illness, create feelings of guilt in people living with serious illness - do you want to add to that burden of guilt?
• Be aware that your urge may be more about dealing with your own distress than genuinely helping them.
• Remember the link between social support and health - the most important help you can give your loved one is to show them that you care about them.