I would like to catch 2 words sequentially duplicated in a pattern

I would like to be able to catch duplicate words in this case `"cancer cervical"` because they are the only duplicate 2 words sequentially. 

pattern `"cancer cervical diane mortality cervical cancer cervical diane sea"` 

I use this Regular expression but still can't catch 2 sequentially duplicated words. 

```
/(\W|^)(.+)\s\2/ig

```