To present a new category of lung carcinoma termed “minimally invasive” adenocarcinoma, give criteria for its definition, and to present data validating such a designation.
164 cases of primary lung adenocarcinomas resected between 1992-2004 were reviewed and divided into 4 groups. Group I: BAC only (49); Group II: Mixed subtype with <<26>5 mm invasive component (16); Group III: Mixed subtype with >5 mm invasive component (63); Group IV: Invasive carcinoma only (36). Tumor size and lymph nodes metastasis were compared. P53 and Ki-67 staining were analyzed in 72 cases (14 from Group I; 9 from Group II; 13 from Group III; 36 from Group IV). The Ki-67 labeling index (LI) was determined by counting 500-1000 tumor cells in three high-power fields (400X) of the most highly labeled areas. P53 overexpression was defined as the presence of nuclear staining in >20% of tumor cells.
Progressively greater lymph node involvement was seen from Group I to Group IV (0%, 0%, 14.8%, 75%). The mean Ki-67 LI (6.2%, 7.5%, 22%, 44.6%) and frequency of p53 overexpression (8%, 11%, 33.1%, 56.3%) also showed an increasing tendency from group I to IV.
Data shows that adenocarcinomas with mixed subtypes (groups II, III) have characteristics between BAC (group I) and purely invasive carcinoma (group IV), supporting the idea that this entity is an intermediate lesion between BAC and invasive cancer. A subgroup of this entity (group II) has characteristics and behavior more similar to BAC, suggesting that this subgroup could be defined as a form of early invasive cancer, and may be clinically managed as such.
An increasing number of lung adenocarcinomas resected fall into this category of mixed subtype adenocarcinoma. Many of them are being treated similarly to purely invasive adenocarcinoma. This data suggests that such treatment is not necessary; more conservative therapy may be mandated.
Joon Yim, None.