Being married, or living with someone, improves lung cancer patients' chance of survival, US experts say.
The University of Maryland team studied 168 patients with advanced non-small cell lung cancer, the most common kind, treated between 2000 and 2010.
A third of patients with partners were alive after three years but just 10% of single patients.
The researchers said living with someone was also likely to offer the same benefits as marriage.
Cancer experts said the research was interesting, but more investigation was needed to assess why there was a link.
The research was presented to the 2012 Chicago Multidisciplinary Symposium in Thoracic Oncology.
All those who took part were treated with chemotherapy and radiotherapy.
Married women had the best three-year survival rate at 46%, while single men had the worst at 3%.
Single women and married men had the same 25% survival rate at three years.
The study was carried out by researchers at the University of Maryland Marlene and Stewart Greenebaum Cancer Center in Baltimore.
Dr Elizabeth Nichols, who led the study, told the BBC: "We hypothesise that being in any stable relationship would result in the same outcome as being married. However, we think this is only the case if the significant other lives with the patient and is with them in a daily basis, and that this is where the true benefit lies."
She added: "Our findings suggest the importance of social support in managing and treating our lung cancer patients.
"Patients may need help with day-to-day activities, getting to treatment and making sure they receive proper follow-up care.
"We believe that better supportive care and support mechanisms for cancer patients can have a greater impact on increasing survival than many new cancer therapy techniques.
Previous research has found single men have a poorer chance of surviving several types of cancer, including prostate and head and neck cancer.
In addition, a Norwegian study found men who never married were 35% more likely to die from cancer than married men. For women, those who never married were 22% more likely to die of cancer than those who were.
Martin Ledwick, Cancer Research UK's head information nurse, said: "This study is interesting, but the numbers of patients included in it were quite small, so further research will need to be done.
"It will also be important to establish what the individual factors are related to marital status that contribute towards any improvement in survival."