The decision about pursuing post-operative treatment is often difficult and requires carefully weighing the risks of treatment with potentially challenging and even dangerous chemotherapy against the potential to eradicate micrometastases and actually lead some people to be cured who otherwise wouldn't be. It's important to remember that some people are already cured, while others won't be cured even with treatment. We're pursuing treatment for the 5-15% higher survival rate at 5 years from adding chemo, presumably representing the proportion of people who have micrometastatic cancer cells that are apparently eradicated by getting 3-4 cycles of platinum-based chemotherapy:

(Click image to enlarge)

The general guidelines we use to assess risk for recurrence include stage of the cancer as the primary focus. I also described the relevance of tumor size as an important factor to stratify risk of recurrence in my recent post on that topic. But there are other potentially relevant factors for people who have cancers that are "on the bubble" about whether they have enough risk to justify the side effects and some real risks of post-operative chemotherapy.

I've covered the topic of tumor grade being predictive of recurrence risk in a prior post. In addition to stage, primary tumor size, and cancer grade, there is the factor of tumor histology subtype (squamous vs. adenocarcinoma). Presumably because of its greater tendency to be associated with micrometastases and spread early, patients with stage I adenocarcinomas (stages IA and IB) have been shown to have a higher risk of recurrence than those with squamous cancers (abstract here):

Remember also that patients with stage I adenocarcinomas also have a higher risk of being "upstaged" by finding unexpected cancer involvement in the mediastinal (mid-chest) lymph nodes, as I described in a prior post. This is the same theme, that squamous cell carcinomas tend to remain localized longer than adenocarcinomas. On the other hand, BAC tumors have a different behavior than invasive adenocarcinomas and tend to be associated with a more favorable survival (described in prior post)(abstract here):

Finally, there is also the minority of patients large cell neuroendocrine carcinomas, who appear to have a less favorable prognosis than other NSCLC subtypes (described in a prior post).

Finally, another factor to consider is the involvement of the visceral pleura, the lining on the outside of the lung. This is reflected in the staging system, since even a smaller tumor that measures less than 3 cm becomes a stage IB NSCLC if it involves the visceral pleura. Here's a survival curve from a series of stage I cancers that shows the difference in survival between those patients who had or did not have visceral pleural invasion (sometimes abbreviated VPI)(abstract here):

So that's a lot of factors from the pathologic report, all worth considering when weighing the pros and cons of chemotherapy after surgery in more boderline cases. And we haven't gotten to imaging factors yet. That's the next topic...