My little sister Flora is about three. She collects chestnuts and pinecones in a small metal box. She stops on walks to smell the flowers as I lean to keep hold of her hand and the greatest problem she has ever had to solve, a 16-piece puzzle. She is a toddler and if my biased opinion is to be trusted, a particularly sweet one at that. She is also the same age I was when my mother was diagnosed with breast cancer.

Insidious thing, cancer. I often thought of it as a completely separate entity from my mum. The uninvited third-wheel in our mother-daughter relationship. But malignant tumours arise from our own cells, so in that sense my mother’s cancer was her. I was once told to think of the disease as a Darwinian process. Species evolve by mutations and natural selection across entire populations; so do cancer cells within each individual. Malignancy is the inevitable cost of our existence as multicellular beings. In the case of my mother, she was in her early thirties when the unwanted bill came. She had no genetic predisposition, no family history; the chances of her getting sick were laughably small. But the cancer grew anyway, and with it, an unnamed bulk of guilt and responsibility which crawled its way onto my then small back. I have flashes of her skinny figure in a vast double bed taller than myself. I doubt I really understood what was happening then, but I know that she underwent surgery and chemotherapy early on. The cancer hid for a while, then in 1999 it came again, this time grafting itself onto her right hip. With the benefit of hindsight and many years of biomedical studies, I now know this was the beginning of the end – once the cancer reaches the bone, there is no way to remove it. From then on, my mother's condition was, plainly, incurable. I have no recollection of being explicitly told this, not then anyway. Any mention of Darwin and oncogenic mutations did not reach me until much later in life. But her first relapse remains brutally etched onto my memory.

In the Christmas break of that year and in the midst of a vicious round of chemotherapy, my parents took my sister and me to a ski resort. I was five, my sister was eight. Much of that holiday is a blur – and hard as I try to recall, I do not believe I was aware of the full extent of my mother’s disease. Shortly after we arrived, she fell sick and was rushed to a doctor nearby. It was when she returned the following night that it dawned on me for the first time in my life: one day parents would die, and I would be alone. I rushed to my mother for comfort. She calmed me down and said not to worry and to enjoy the rest of the holiday. But a few days later on New Year’s Eve, while I was jumping around to songs I didn’t really know, thoughts of my mother’s health came back to haunt me, mingled with a dull feeling I could not quite put words on. As the millennium drew to a close, I was joined by a shadow that would stalk me for the rest of my life.

The thought that I’d burdened my mother with my own fears was mortifying; what pain she must have felt, knowing the cancer was killing her even as she consoled me. I never mentioned the incident again. Instead, I quietly carried the shame of what I considered my pathetic failure to deal with my mother’s terminal illness without causing a scene. And as the cancer cells continued to slowly but inexorably multiply inside of her, so did my own feelings of guilt.

For the twelve years that followed, the cancer lived with us like an unwanted family guest we all did our best to ignore. Occasionally, it disappeared for a while before storming back in, each remission shorter than the last. The cycle became so familiar that I fooled myself into thinking it would carry on forever. I went about my life as normally as I could. I went to school, I sang in a choir, I took violin lessons - and convinced myself that things would get better, eventually. Yet at times, the horrors of my reality burst through that naive ignorance, just as they had in 1999.

When I was around twelve, my mother lost her hair. It had happened before several times, but her most recent chemotherapies had spared her this characteristic side-effect and I had almost forgotten what she looked like bald. I was the only one home when she came from the hairdresser, where she’d said goodbye to the last remaining clumps of hair not yet ravaged by the medication. I assured her she looked great, that her new black chemo hat was cute and that we’d find a good wig anyway but was unable to mask my reaction upon seeing her. She looked so small. So ill. All I could see was her cancer. I knew how upset she was at losing her hair again and hated myself for hating her appearance and for the half-second in which I feared the shock had been visible in my eyes.

While writing this piece, I found an email I’d sent that same year to a teen magazine in response to a story about cancer they had recently published. Written in Comic Sans and signed off with a smiley face - my attempt to lighten the mood - the message read:

“My mother has had cancer since I was two years old. I have learnt to live with it, but the older I get, the harder I find it. I am unable to talk about it with my mother, nor my family, nor a psychologist nor my friends. How can I make it easier and help my mother?”

:-) Emma, 12 (Paris)

I received a very kind email back, five days later. The editor suggested I look to artistic outlets as a coping mechanism: “drawing, writing.” As it turns out, I had spent most of my childhood writing. Short poems, mainly, though I ventured into other genres too. At primary school, I’d penned a small pamphlet in which I examined the meaning of words. In suitably morbid fashion, the first one on the list was "death". I wonder what my parents made of it.

When I was fourteen, my mother once asked me to pick up the results of a blood test for her, too anxious to see what they might show. Unfolding the piece of paper in the laboratory’s drab green waiting room, I broke down. I willed the numbers to change but the stubborn un-solvability of her illness stared back at me from the page. I called my father in tears. After all the pain and the treatments, how could I possibly tell her she was still dying? In the end, it was she who had to comfort me. Here I was, five years old again, unable to cope and unable to make her better. “So it’s not so good, is it?” she said as I opened the front door. “It’s ok, the doctor said the markers might continue going up for a bit.”

A month prior to her death, I went on a trip with my conservatoire orchestra. In hindsight I should have known when cancerous nodules were found in her liver not long before, that time was fast running out. Still, celebrating Halloween in various bars of Vienna, the cancer seemed far away. And nothing quite takes your mind off impending death like a week of underage drinking and sleep-deprived performances of Verdi's Requiem. Reality came crashing down the same hour I got back. My father came to pick me up from the coach station on the way to collect my mother up from a therapist appointment. She climbed into the car and burst into tears. “I am not afraid anymore,” she told my dad. It wasn’t until two weeks later when my father sent me to stay with my grandparents to shield me from the excruciating final moments, that I understood what she had meant. We had finally reached the end. After fourteen years of a life-threatening illness, I still failed to recognise death when it came.

For a long time after her passing, I dreamt about her often and every time the same scenario would play out. I would see her on a Metro platform in Montparnasse, near our flat in Paris, and I would apologise for not realising early enough that she was about to die. My mother was gone, but my guilt remained.

In the gaping hole she left behind, I found solace in biology textbooks. I relished learning anything to do with cancer. I sought any mentions of the chemotherapy drugs I had seen my mother endure. Taxol. Taxotere. Any mutations I remembered hearing about. HERC2. BRCA1. “Bones are the most common metastatic site for breast cancer”. “Secondary liver tumours develop in about half of all metastatic breast cancers and often lead to liver failure”. Rather than finding it upsetting, it was like a comforting voice making sense of it all. Here for the first time was a logical justification for my illogical childhood, a coherent explanation of my mother's illness.

Biology gave me another, more unexpected source of healing. The same year my mother died, I took an internship at a laboratory researching cancer in Tasmanian Devils. It was there that I first learnt about malignant tumours in the context of evolutionary theories. The scientist who supervised me called them “biological dead-ends” – once the cancer becomes stronger than its host, it dies with them; just like my mother’s cancer had disappeared with her. In the months that followed, that same scientist met my dad who’d wanted to thank her for taking good care of me. They married some years later. And so in a strange turn of events, after cancer took my mother, it gave me a younger sister, Flora.

It has been eleven years now since my childhood fear of losing a parent came to pass. My own thirties are looming large on the horizon. Flora, on the other hand, is looking forward to her fourth birthday. A few weeks ago, she became inconsolable after breaking a small plate and as I comforted her, I saw my own childhood expectations beginning to crumble too. I had always believed it a perfectly reasonable assumption that I should know to deal calmly with my mother’s illness before I had even learnt how to read. All those failures I’d been carrying around since I was Flora's age, my remorse, my guilt - it was justified. Now, faced with the reality of a toddler’s emotional landscape, I realised for the first time the sad absurdity of it all.

It took over a decade and the arrival of Flora into my life, to reach that basic conclusion. Sometimes in her eyes, I recognise the same carefree innocence I traded as a child for a lifetime of self-reproach. I cannot change how I grew up, nor, as I assured my mother on her deathbed and many times in dreams, would I have wanted to. But as I watch Flora play with her toys and cry over broken crockery, the burden of guilt medical textbooks never quite managed to shift slowly makes way for bittersweet relief. I was a kid who did not know how young she was. I did my best in the worst of scenarios; one day I will accept that that was enough.