Cell migration leads to spatially distinct but clonally related airway cancer precursors

Abstract

Background: Squamous cell carcinoma of the lung is a common cancer with 95% mortality at 5 years. These cancers arise from preinvasive lesions, which have a natural history of development progressing through increasing severity of dysplasia to carcinoma in situ (CIS), and in some cases, ending in transformation to invasive carcinoma. Synchronous preinvasive lesions identified at autopsy have been previously shown to be clonally related.

Methods: Using autofluorescence bronchoscopy that allows visual observation of preinvasive lesions within the upper airways, together with molecular profiling of biopsies using gene sequencing and loss-of-heterozygosity analysis from both preinvasive lesions and from intervening normal tissue, we have monitored individual lesions longitudinally and documented their visual, histological and molecular relationship.

Results: We demonstrate that rather than forming a contiguous field of abnormal tissue, clonal CIS lesions can develop at multiple anatomically discrete sites over time. Further, we demonstrate that patients with CIS in the trachea have invariably had previous lesions that have migrated proximally, and in one case, into the other lung over a period of 12 years.

Conclusions: Molecular information from these unique biopsies provides for the first time evidence that field cancerisation of the upper airways can occur through cell migration rather than via local contiguous cellular expansion as previously thought. Our findings urge a clinical strategy of ablating high-grade premalignant airway lesions with subsequent attentive surveillance for recurrence in the bronchial tree.

Keywords: Airway Epithelium; Lung Cancer.

Figure 1

Spread of the TP53 p.E294fs*51 mutant clone (exon 8) over time in patient 1. The mutant clone (red circle/filled red circle) was first detected at M₃₈ in the left upper lobe (LUL) stump and spread over 142 months (M₃₈–M₁₈₀) in a distal-to-proximal direction towards the MC and trachea and then over into the right lung. Control biopsies from autofluorescence bronchoscopy-negative areas confirmed histologically normal and genetically wildtype intervening epithelium (shown as black star or filled black star). The part of the lung surgically removed by lobectomy (dashed black line, LUL stump) is not shown. Completion pneumonectomy (M₉₁) is depicted as a solid black line.

Figure 2

Tracing of the common mutant clone over time in the tracheobronchial tree of patient 2. Tracing the TP53 c.725G>T clone (exon 7) over 42 months from the left lower lobe stump (M₄₃) to the trachea (M₈₅). A second, unrelated tumour (K-RAS c.262G>T) was detected in the right lower lobe at M₅₀.

Figure 3

Tracing of the common mutant clone over time in the tracheobronchial tree of patient 3. Distal-to-proximal spread of the c.517G>T clone (TP53 exon 5) within 29 months from the left upper lobe stump (M₈) to the trachea (M₃₇). The clone must have arisen at the lower trachea earlier than M₃₇.

Figure 4

Tracing of the common mutant clone over time in the tracheobronchial tree of patient 4. Detection of the c.517G>T and c.469G>T mutations (both TP53 exon 5) at the right upper lobe stump (M₁₁). Only one mutation was detected at the posterior wall of the trachea (M₁₁), suggesting this was the first mutation and these cells spread towards this site before the second mutation occurred.

Figure 5

Tracing of the common mutant clone over time in the tracheobronchial tree of patient 5. Simultaneous detection of the c.724T>C and c.731G>A clones (both TP53 exon 7) at the lobectomy stump 50 months postsurgery (M₅₀) and distal-to-proximal spread towards the lower trachea.

Figure 6

Proposed mechanisms of clonal spread of carcinoma in situ in the lung epithelium. (A) ‘Field of injury’. Growth of clonally unrelated, multifocal lesions within a field predisposed to the same change after exposure to a common damaging agent. (B) ‘Contiguous field’. Continuous expansion of a clone, giving rise to a patch of clonally related cells and formation of a progressively expanding contiguous field. (C) ‘Cell breakaway and migration’. Following formation of a ‘clonal unit’ from an initial cell that acquired a proliferative advantage through acquisition of a mutation, a cell or group of cells breaks away from the unit and migrates via histologically normal and genetically wildtype epithelium in order to establish new lesions within a suitable niche.