In June 1961, Karen was diagnosed with a malignant tumor of the middle part of her brain stem; X-ray treatment slowed its growth, but her health deteriorated to the point where she could no longer walk or talk.
En xuño de 1961 a Karen diagnosticóuselle un tumor maligno na parte media do seu tronco cerebral; o tratamento con raios X ralentizou o seu crecemento, pero a súa saúde deteriorouse ata o punto de que deixou de andar e falar.