What is the grading code for a poorly differentiated squamous cell carcinoma found in a lymph node from a lung primary?

The correct grading code for a poorly differentiated squamous cell carcinoma found in a lymph node from a lung primary is B, which corresponds to G3 Poorly differentiated.

In the grading system for tumors, differentiation refers to how much the cancer cells resemble normal cells of the tissue from which they originated. Poorly differentiated tumors (G3) do not closely resemble normal tissue and typically display more aggressive behavior compared to moderately differentiated (G2) or well-differentiated tumors.

Undifferentiated cancers (G4) are entirely unrecognizable as any specific tissue type, while grade X (GX) suggests that there is insufficient information to determine the grade. In this case, since the carcinoma is identified as poorly differentiated, the appropriate code that accurately reflects its differentiation status is G3. Thus, G3 is the designation that denotes the level of differentiation and the biological behavior of the tumor effectively.