Objective: The objective of this study was to explore the lived experiences of mothers caring for young adults (AYAs) diagnosed with sarcoma using an existential phenomenological approach. Methodology: Nine mothers participated in conversational interviews, guided by their narratives. Reflexive thematic analysis, informed by Van Deurzen's four existential dimensions (Umwelt, Mitwelt, Eigenwelt, and Uberwelt), identified themes within and across interviews. Findings: The findings highlight that mothers' experiences could be thematized into three domains with associated themes. These domains intersected with the four aforementioned dimensions with the context of living through a sarcoma diagnosis. The main themes were: Mothers oscillate between the everyday world organised by their day-to-day responsibilities and the healthcare system. The demands of living with a sarcoma diagnosis creates a sense of displacement and isolation for mothers. However, they find support and connection through a "sisterhood" with other mothers facing similar experiences. Mothers experience a range of emotions – shock, fear, and grief. They have to grieve an unthought future for their child, while confronting the potential loss of their child in the here and now. The experience transforms mothers' worldviews, leading to a deeper appreciation for life and a stronger sense of self. Conclusion and Implications: The findings call for a biopsychosocial approach to healthcare, integrating psychosocial support into cancer care for both patients and caregivers.