I just did a search on the term "MO" and "M0"...I got an AI response for "MO" (letter "O") as follows (not what I thought it would be, and likely several of you out there as well):

"MO" on a surgical pathology report typically stands for "margin of resection." It indicates the status of the surgical margins in relation to cancerous tissue.

Key Points:
Definition: "MO" refers to the evaluation of whether cancer cells are present at the edges of the tissue that was removed during surgery.
Importance: Clear margins (no cancer cells at the edges) suggest that the cancer has been fully excised, while positive margins (cancer cells present) may indicate a need for further treatment.
Context: This term is crucial for determining the prognosis and potential next steps in treatment.
Understanding the status of the margins helps guide further management decisions in cancer care." And...

The search for "M0" ("0" being a "zero") means: "M0 = No metastases" as one reviewer commented here. Just more confusion...why would they use both "MO" and "M0" in surgical pathology jargon to define something??? Crazy.