My Mum Recently Passed In October, She Was Treated For

My Mum recently passed in October, she was treated for COPD and asthmas, fibromyalgia for over 20 years, she was last in hospital in 2013 for treatment of pneumonia which was reoccurring , in August 2015 she was admitted to hospital with pneumonia again however it was sepsis, after 4 weeks she got of live support but had grade 4 liver and bone cancer which ultimately killed her in October which the primary tumour was in the lung. how could this happen so quickly, can it happen that cancer primary in the lungs then liver and bone can result in death within a year and a half and go undiagnoised.