Is Adenocarcinoma Very Harmful?

My husband lifted a heavy object, felt back pain which didn t require immediate treatment. After about 10 days he saw his Dr. stating he must have pulled a muscle (something experienced more than once through his life). Muscle relaxers and prescription Advil didn t help. Prior to seeing the Dr. and for a few days after, he had painted our entire condo inside and plowed driveway snow. He then had an X Ray, followed by a lower spine MRI which showed lesions. Then came a nuclear bone scan which showed Metastatic lesions needing more identification. A Pet Scan was scheduled but by then he was on the sofa all day unable to sit or stand. The scan never took place. He went by ambulance on 2/23/14 to the hospital, in pain but with his usual sense of humor. He spent 12 days in the hospital. A biopsy and full body MRI confirmed lung cancer which had spread to his liver and spine. It was too far gone for radiation. On the 13th day he was sent to a hospice where he spent 29 hours, then died. When dealing with his sudden death I feel he was cheated by not having more of a warning during the prior months or was he just too strong to recognize it? Maybe this cancer (adenocarcinoma) is just so aggressive and we should be glad he went quickly with minimal suffering but my grief is expressed more in anger than in tears of emotion. Can you comment to help me understand? Thank you.