It appears that this is commonly initially misdiagnosed globally, especially in low incidence areas.
Laryngeal tuberculosis often presents as a tumorous mass that may initially be mistaken for cancer. As laryngeal tuberculosis is usually highly infectious, this poses a risk to the patient as well as his/her contacts including healthcare providers. (National Library of medicine, Netherlands)
Routine BCG vaccine is no longer offered to children in secondary schools in the UK. It was replaced in 2005 with a targeted programme for babies, children and young adults at higher risk of TB. This is because TB rates in this country are very low in the general population.
In a growing number of European countries, BCG vaccination has been discontinued or has been limited to children 'at risk', such as those born in or originating from countries with high prevalence. Additionally, BCG revaccination has been progressively abandoned.
I suspect that as usual, Fanny is putting her own spin on this and especially on the timeline. I think Percy was showing signs of this before leaving SA and his sons may have already ben aware that this could have been cancer/TB.