When I think about a bone marrow biopsy, I often imagine a microscope. I imagine it sitting on the desk of an empty hospital lab. A doctor is looking into the eyepiece and not saying anything. What does he see in there?

I’ve been thinking a lot about the number 100 since my bone marrow transplant in July. The date had been looming since the first days after I had woken, though it also felt like it would never come. In medical terms, the 100 day mark is an examination day. It’s the first major benchmark for evaluating a patient’s recovery from a transplant. The doctors administer a biopsy, an invasive procedure to extract bone marrow from a bone in my hip, to determine whether the disease has returned. The doctors are also looking for any sign that the “foreign” agents in my body — the donor stem cells, mistakenly attacking my body. This condition is called Graft Versus Host disease (GVHD).  My worry right now is about what I can’t see — the stuff under the microscope.

In some ways, 100 days is an arbitrary date — even my doctors might concede that. It could be 80 days or 175. Recovery from bone marrow transplants, as I’ve learned from doctors and fellow cancer patients, is rarely predictable. I have a 28-year-old friend who says she “sailed through” the first 100 days after transplant without major issue, only to reveal that her hardest days came in the second 100 days. Maybe that’s the reason, as another friend and transplant patient said recently, that there aren’t a lot of books titled, “How to Recover From a Bone Marrow Transplant.” It’s one of the most advanced medical procedures that doctors do — and it seems as though each patient’s journey is likewise a step into unknown territory.

Maybe more than anything else, the 100 day mark is symbolic. And maybe that’s not a bad thing. My family threw me a party last Saturday, on Day +101. We had cake — the number 100 frosted across the top — and everyone stumbled through a variation of the “Happy Birthday” song that we had to make up on the spot. It was the first time I’d seen my family together since my transplant.

Two days after the party, on Monday, I started a new round of chemotherapy. The doctors want to prevent any cancerous cells from exacerbating. That makes sense, but it’s hard to think about recovery from my transplant when I am trying to prepare for another year of chemo.

The 100 day party may be over but I’m trying to find a moment to take stock of the progress I’ve made since my transplant.