Table 2.
Comparison of tumor‐infiltrating lymphocytes (TILs) between primary and metastatic breast cancer tumors for each subtype
| Subtype | First site of biopsy | Primary tumor TILs, % | Metastatic tumor TILs, % | Comparison |
|---|---|---|---|---|
| HER2+ | Bone marrow | 10 | <10 | → |
| Brain | 20 | <10 | ▼ | |
| Brain | <10 | <10 | → | |
| Brain | 80 | 10 | ▼ | |
| Brain | <10 | 10 | → | |
| Brain | 30 | 50 | ▵ | |
| Liver | 60 | 10 | ▼ | |
| LN (Ax) | 50 | 20 | ▼ | |
| LN (rotter) | 70 | 20 | ▼ | |
| LN (SCLN) | 70 | 10 | ▼ | |
| Lung | 10 | <10 | → | |
| Muscle (pectoralis) | <10 | 30 | ▵ | |
| Skin (thoracic wall) | 30 | <10 | ▼ | |
| Skin (thoracic wall) | <10 | <10 | → | |
| TN | Bone | 10 | 20 | → |
| Bone | 20 | 20 | → | |
| Brain | 50 | <10 | ▼ | |
| LN (rotter) | 70 | <10 | ▼ | |
| Lung | 10 | 50 | ▵ | |
| Lung | 30 | <10 | ▼ | |
| Skin (abdominal wall) | 80 | 30 | ▼ | |
| Skin (head) | 10 | <10 | → | |
| Skin (thoracic wall) | <10 | <10 | → | |
| Skin (thoracic wall) | 50 | 20 | ▼ | |
| Skin (thoracic wall) | 80 | 10 | ▼ |
The percentage of TILs in the primary tumors was significantly higher (average, 34.6%) than in the metastatic tumors (average, 15.7%) (paired t‐test, P = 0.004). This difference was similar in the human epidermal growth factor receptor 2 (HER2)+ (P = 0.036) and triple negative (TN) (P = 0.06) breast cancer groups. Ax, axillary lymph node; SCLN, supraclavicular fossa lymph node.