Types of occult cancer in stroke and the relation to smoking

Stroke is associated with a higher risk of occult cancer. We studied the types of occult cancer most often associated with stroke.

All patients with incident stroke in Denmark 2003-2015 were identified through the Danish Stroke Registry (n = 85 893) and matched 1:10 on age and sex to the Danish background population without history of stroke (n = 858 740). Linking data to the Danish Cancer Registry, we determined the prevalence of occult cancer in stroke defined as the event of previously unknown cancer during a one-year follow-up in the stroke and the background population. We stratified cancers into the 15 most common cancers and into cancers related to and not related to smoking.

Prevalence (per 1000 person-years; stroke/background population) of smoking-related occult cancers (lung, colon, bladder rectum, pancreas, kidney, stomach, and head and neck) was 13.3/8.1 (P < .01) and of cancers not related to smoking (prostate, breast, melanoma, non-Hodgkin lymphoma, ovary, endometrial) it was 6.6/6.2 (P > .05). Among men with stroke prostate (5.8), lung (5.7), and colon cancers (2.9) were most frequent; among women, it was lung (4.7), breast(3.5), and colon cancer(2.8). Among men in the background population, prostate(5.4), lung (3.0), and colon cancers (2.1) were most frequent. Among women, it was breast (3.7), lung(2.1), and colon cancers (1.9).

Stroke patients' increased risk of occult cancer was predominantly for smoking-related cancers while there was no higher risk for the most frequent cancers unrelated to smoking, that is, prostate and breast cancers. Lung cancer is the dominant type of occult cancer in stroke.